WO2002040411A1

WO2002040411A1 - A remediation method of contaminated materials by using zeolite anchored nanoscale iron containing reactive wall

Info

Publication number: WO2002040411A1
Application number: PCT/KR2000/001309
Authority: WO
Inventors: Jae-Won Lee; Jun-Boum Park; Seung-Hak Lee; Il-Chul Jung; Si-Hyun Kim; Sang-Su Lee
Original assignee: Halla Engineering & Industrial Developement Co., Ltd.; Geo Works Co., Ltd
Priority date: 2000-11-16
Filing date: 2000-11-16
Publication date: 2002-05-23
Also published as: JP3976679B2; JP2004524947A

Abstract

The present invention relates to a remediation method of contaminated materials by using zeolite anchored nanoscale iron comprising the steps of making a reactive wall including zeolite anchored nanoscale iron and installing the reactive wall at the place where contaminate materials pass, and eliminating contaminant by passing contaminated materials through the reactive wall. According to this invention, the remediation of organic chlorides by granular iron and remediation of heavy metals and nutrient salts by zeolite can be carried out in a single reactive wall system.

Description

A REMEDIATION METHOD OF CONTAMINATED MATERIALS BY USING ZEOLITE ANCHORED NANOSCALE IRON CONTAINING REACTIVE WALL

Technical Field

The present invention relates to a remediation method of contaminated materials by using reactive wall and, more particularly, to a remediation method of contaminated materials by using reactive wall built under the ground where contaminated materials exist, whereby contaminated materials are eliminated by the chemical reaction of reactive media and contaminated material is induced by hydraulical flow of contaminant band of underground water. More specifically, the present invention uses, as reactive media of reactive wall, zeolite anchored nanoscale iron so that the remediation of organic chlorides by granular iron and remediation of heavy metals and nutrient salts by zeolite can be carried out in a single reactive wall system.

Background Art

In conventional ways of building a reactive wall for remediation of contaminated underground water, granular iron has been used as reactive media. For instance, USP 5,575,927 discloses a method for faster reduction of halogenated hydrocarbon by the use of mixture of iron and fen-ous sulfide in relative quantities as reactive media than when either of these materials is used separately. And, USP 5,543,059 discloses a method for purification by passing contaminated material containing halogenated hydrocarbon through a tiered iron wall or column, comprising at least three zones of granule size of iron particles as reactive media.

Above referenced conventional prior arts are characterized by removing contaminated material by subjecting the underground flow of water mixed with contaminated material to pass through a reactive wall of iron granules, with no particular additives added thereto, built at strategic points for natural interception.

In above referenced prior arts, the mechanism for removal of contaminated materials by elemental iron is known as follows:

Iron existing as Fe° undergoes oxidation, forming redox couples. It resembles the corrosion caused by a spontaneous oxidation of elemental metals, which have a tendency to lose electrons and to be in a cationic state. In the case of iron its redox potential is - 0.44V.

Fe° <-» Fe² + 2e^" Formula (1)

FigJ is a diagram of the process of dechlorination of PCE (C₂C1₄, tetrachloroethylene) and its standard redox potential. In Fig. 1, dechlorination becomes slower, as it is farther from B to A. C indicates the point where the oxidation rate is highest and D, the point where it is lowest. As can be anticipated from Fig. 1, major reductants capable of reacting with organic chlorides are Fe°, Fe²⁺, and H₂. For instances of corrosion, the reaction is generally achieved by direct electron exchanges between Fe° and al yl chlorides adsorbed on the surface (Formula 2) but the reaction also may occur by Fe²⁺ produced from the corrosion (Formula 3), H₂ (Formula 4), and H₂O, etc.

Fe° + RX + H⁺ <→ Fe²⁺ + H + X^" (Formula 2)

2Fe²⁺+ RX + H⁺ <-> 2Fe³⁺ + RH + X^" (Formula 3)

H₂ + RX <→ RH + H⁺ + X^" (Formula 4)

Fig. 2 shows the reductive dechlorination of organic chlorides by exchange of electrons in corrosion of Fe°; Fig. 2A showing the reductive reaction of organic chlorides by Fe° which occurs on its surface; Fig. 2B, the reductive reaction of organic chlorides which occurs indirectly by way of ferrous ions; while Fig. 2C shows the role played by Fe° in the reductive reaction of organic chlorides by H₂ in the presence of catalyst.

In addition, it is known that zeolite can remove nutrient salts such as ammonia nitrogen etc., and heavy metals such as cadmium, lead, copper and zinc etc., from the contaminated materials by ion exchange. The ion exchange here means that ions which have charges existing in liquid state are selectively exchanged with ions which have same kind of charges existing in solid state. It is possible to separate and eliminate specific ion by this exchange reaction. The ion exchange reaction is performed stoichiometrically and makes recycling of materials possible since basic structure of the solid in which ions are exchanged remains unaffected.

Assuming the ion exchange mechanism is a binary system which consists of the specific ion (NH₄ ⁺) in liquid state and the ion (Na⁺) in solid state (Z) to be exchanged, the exchange reaction of (Na⁺) ion in Z and (NH₄ ⁺) ion in an aqueous solution is represented by the following formula.

Z-Na⁺ +NH₄ ⁺ = Z-NH₄ ⁺ + Na⁺ (Formula 5),

where Z represents zeolite such as the body of clinoptilolite. Ion exchange occurs at certain place called pore (see Fig. 3) and, in the case of clinoptilolite the size of pore is known to be 4A.

But, the conventional reactive wall methods, as mentioned above, can be applicable only to the contaminated materials such as PCE, TCE, DCE, VC, CT and the like, but cannot be applicable to the contaminated materials such as PCBs which needs high redox potential, and other heavy metal and nutrient salts, because the granular iron has limited redox potential when used without additional treatment or addition of other materials. Furthermore, another problem is that the zeolite has been conventionally used in the way of directly adding to aqueous solution and applicable materials are limited to heavy metals and nutrient salts.

Summary of the Invention

In order to solve the problems as mentioned above, one object of the present invention is to provide a remediation method using reactive wall filled with singe material, which can eliminate, in a single reactive wall system, the organic chloride compound which can be eliminated by conventional reactive wall including elemental granular iron and heavy metals and nutrient salts which can be eliminated by zeolite, minimizing the thickness of reactive wall and solving the problem of phase separation of zeolite and iron due to the difference of specific gravity.

The remediation method of contaminated materials by using zeolite anchored nanoscale iron of the present invention comprises the steps of making a reactive wall including zeolite anchored nanoscale iron and installing the reactive wall at the place where contaminated materials pass, and eliminating contaminant by passing contaminated materials through the reactive wall. In the zeolite anchored nanoscale iron, the zeolite is the material that can remove nutrient salts such as ammonia, nitrogen and phosphorus and heavy metals such as cadmium, lead, copper and zinc by ion exchange mechanism, and includes clinoptilolite which is a sort of natural zeolite. As can be seen in table 1, SiO₂, the main ingredient of zeolite, can function as a functional group that makes the form of zeolite anchored nanoscale iron by making Fe combine with zeolite.

The zeolite of the present invention can be prepared by the process comprising the steps of;

(i) cleaning zeolite with distilled water for 3 hours; (ii) soaking the zeolite cleaned in step (i) into HNO₃ of IN for 3 days and cleaning the zeolite with degassed water;

(iii) putting the zeolite cleaned with degassed water into the 1.0M ferric chloride

(FeCl₃-6H O) solution whose pH was neutralized by NaOH, and stirring the solution strongly for more than 10 hours; (iv) pouring out the clarified supernatant liquid of step (iii) carefully and pouring in

0.5mM NaCl solution, and maintaining the solution for 24 hours;

(v) repeating the step (iv) 5 times; and

(vi) drying the obtained zeolite which is chemically adhered with nanoscale iron.

The zeolite of the present invention can also be prepared by the process comprising the steps of;

(i) cleaning zeolite with distilled water for 3 hours;

(ii) putting the zeolite cleaned in step (i) into 1.0M ferric chloride (FeCl₃-6H₂O) solution and infiltrating the ferric chloride (FeCl₃-6H₂O) solution into the inner structure of zeolite by stirring slowly for 2 hours;

(iii) inducing the precipitation of Fe° as in formula (6) inside the structure of the zeolite by adding 1.6M of sodium borohydride liquid into the solution of (ii) while stirring the solution, Fe(H₂O)₆ ^3"+ 3BH₄ ^" + 3H₂O→Fe°| + 3B(OH)₃ + 10.5H₂ Formula (6).

The nanoscale iron in the precipitation obtained as above combines strongly with zeolite, for example, with the oxide existing on clinoptilolite, and securely anchored inside the zeolite in the fomi of Fe°. Fig. 3 illustrates the structure of zeolite anchored nanoscale iron.

As can seen from Fig. 3, nanoscale iron 20 is anchored on zeolite by the combination with SiO which exists outside the structure of zeolite.

The zeolite of the present invention can also be prepared by the process comprising the steps of:

(i) cleaning zeolite with distilled water for 3 hours;

(ii) impregnating 2g of zeolite into 500ml of ferric nitrate (Fe(NO₃) -9H₂O) solution with concentration 0.5-2M and stirring the solution for 24 hours;

(iii) cleaning zeolite with deionized water after pouring out the clarified supernatant liquid of step (ii);

(iv) repeating step (ii) and step (iii) four times;

(v) drying zeolite of step (iv) at 80^°C; and (vi) burning zeolite of step (v) at 450 ^°C .

The contaminated materials to which the method of present invention can be applied include organic chlorides such as PCE(C₂C1₄, tetrachloroethylene), TCE(C₂HC1₃, trichoroethylene), DCE(C₂H₂C1₂, dichloroethylene), VC(C₂H₃C1, vinyl chloride), CT(CC1₄, carbon tetrachloride), trichloromethane(CHCl₃), dichloromethane(CH Cl₂), chloromethane(CH₃Cl) and PCBs(polychlorinated biphenyls). These materials are changed into harmless material such as ethane by reductive dehalogenation reaction which replaces CI^" ion with H⁺ ion by the electron generated in the corrosion of Fe°.

The reactive wall which includes zeolite anchored nanoscale iron is built in the trench which was prepared at the site by using backhoes and clamshells. In the zeolite anchored nanoscale iron, normal soil and excavation soil are mixed according to the mixture ratio determined from the measurement of permeability coefficient calculated in the below examples. In the process of mixing, the mixture is mixed directly by using mixing plant and poured into the trench. While pouring reactive media into the trench, steel sheet pile can be penetrated temporarily for securing the trench.

In mixing the zeolite anchored iron and mixture soil, the maximum content of nanoscale iron is the amount that can prevent too much reduction of permeability coefficient due to the clogging of the air gap, and the minimum content of nanoscale iron is the amount that can sufficiently eliminate contaminant according to the degree of contamination. Preferably, the content ratio of nanometer scale iron in the reactive wall materials including sandy soil is 5 ~ 20 wt%, and most favorably 20wt%.

By using the reactive wall including zeolite anchored nanoscale iron, the organic chloride compound which can be eliminated by conventional reactive wall, and heavy metals and nutrient salts which can be eliminated by zeolite can be eliminated in a single reactive wall system.

Brief Description of Drawings

Fig. 1 shows the process of dechlorination of PCE and the standard redox potential;

Fig. 2A shows the reductive reaction of an organic chloride compound directly taking place on the surface of elemental iron;

Fig. 2B shows the role of elemental iron in a reductive reaction of an organic chloride compound indirectly taking place by ferrous ion;

Fig. 2C shows the role of elemental iron in a reductive reaction of an organic chloride compound taking place by H₂ in the presence of catalyst;

Fig. 3 shows the structure of zeolite anchored nanoscale iron;

Fig. 4 shows the change of the permeability coefficient according to the content of zeolite anchored nanoscale iron in example 1 A;

Fig. 5 shows the change of concentration of PCE in the lOO^M solution of PCE in example 1; and

Fig. 6 shows the change of concentration of ammonia (NH₄ ⁺) ion in example 2.

Examples The present invention will now be described in more detail through examples. The examples, however, are for the purpose of illustration only and are not intended to limit the invention.

Example 1

A. Evaluation of the permeability coefficient of the reactive media

The zeolite anchored iron, the reactive material of the present invention, and soil are mixed with weight ratio of 10:90 (reactive material : soil), 20:80 (reactive material : soil),

30:70(reactive material: soil) and 50:50 (reactive material : soil), and then the permeation coefficient is evaluated by hydrostatic head permeability test method of Korean standard

KSF-2322. The test method is as follows:

(1) Reactive material is prepared as a sample to measure the permeability coefficient and its weight is measured.

(2) The cross sectional area is calculated by measuring inner diameter of the percolation pipe.

(3) The percolation pipe is placed on perforated plate and fixed thereon.

(4) Brass wire mesh is placed on bottom plate of the vessel. (5) The sample is filled in the pipe up to 10cm of height, hardened uniformly with a tamping bar, and the height (L) of the sample is measured.

(6) The weight of the sample in the pipe is calculated by subtracting the weight of remaining sample from the weight of sample measured in step 1.

(7) The specific gravity and moisture content of remaining sample are measured. (8) The pipe with sample is saturated with water.

(9) Water is poured through the upper end while maintaining water level uniformly by overflowing the water through the overflow hole on the upper portion of the pipe.

(10) Water is drained by opening draining outlet on the lower portion of the pipe while maintaining water level uniform, and the system is maintained until the amount of overflowing water is constant.

(11) The amount of draining water (Q) and time (t) is measured.

(12) The head difference (h) of the top and bottom of the sample is measured.

(13) The temperature (T) of water is measured

(14) Moisture content of sample tested is measured after the experiment. (15) The permeability coefficient is calculated by following equation.

where, k = permeability coefficient(cm/sec), L = length of the sample(cm), A = cross section of the sample(cm²), h = head difference of the static (cm), t = percolation time(sec) Q = amount of penetrated water(cm³).

The result of the example 1A is shown in Fig. 4. As shown in the figure, when the content of the zeolite anchored nanometer scale iron is 10 wt% or 20 wt%, there is substantially no reduction of permeability coefficient as time elapses. On the other hand, when the content is 30wt% or 50wt%, permeability coefficient is remarkably reduced as time elapses. The reason may be the clogging of the air gap by zeolite anchored iron due to the high content of zeolite anchored nanoscale iron.

B. Evaluation of the elimination effect of PCE according to the invention.

In this example, the reactive wall containing zeolite anchored nanoscale iron and sandy soil of the weight ratio 20: 80 is built with 1 m in width, 0.5 m in depth and 0.01m in thickness and aqueous solution with PCE concentration 100 is passed through the wall. The effect of remediation of contaminated materials by using zeolite anchored nanoscale iron of the present invention is evaluated by measuring the PCE concentration of passed aqueous solution as time elapses.

The permeability coefficient of the reactive wall containing zeolite anchored nanoscale iron is measured as 5cm/hr and the hydraulic gradient 1/50. Darcy flow velocity calculated from this result is OJcm/hr and the maximum flow velociy of the underground water for evaluation of this invention was set as lcm/hr which is ten time the Darcy flow velocity.

The concentration of PCE used in this example is analyzed by gas chromatography (6890 series, Hewlett Packard Co. U. S. A.). Table 1 shows the analysis conditions of gas chromatography.

Table 1: analytic conditions on gas chromatography

Fig. 5 is shows another result of this example, illustrating the change of concentration of 100 PCE in the solution. As shown in the figure, 80% of PCE is eliminated after 100 hours.

As can be seen from the result, PCE, a kind of organic chloride, is effectively eliminated from contaminated materials by using the reactive wall containing zeolite anchored nanoscale iron.

Example 2

In this example, the aqueous solution with concentration of ammonia 4ppm is used to evaluate the effectiveness of eliminating nutrient salts. The condition is the same as that of example 1 except that the concentration of ammonia is analyzed by using ion chromato graphy.

Fig. 6 shows the result of this example. As shown in the figure, ammonia(NH₄ ⁺) ion is replaced with Na⁺ or Ca²⁺ and 87.5% of ammonia ion is eliminated after 18 hours. As can be seen from the result, ammonia ions, a kind of nutrient salts, are effectively eliminated by using reactive wall containing zeolite anchored nanoscale iron.

Industrial Applicability

The present invention can be used in environmental industries, such as land environmental industries. The present invention can also be applicable to industrial estates and military facilities such as underground oil storage facilities, semi-conductor plants, areas of heaving populated with plants, petrochemical engineering facilities, etc. for instance.

Claims

ClaimsWhat is claimed is:

1. A remediation method of contaminated materials by using zeolite anchored nanoscale iron, comprising the steps of: making a reactive wall including zeolite anchored nanoscale iron and installing said reactive wall at the place where contaminated materials pass; and eliminating contaminant by passing contaminated materials through said reactive wall.

2. The remediation method of contaminated materials by using zeolite anchored nanoscale iron according to claim 1, wherein said zeolite anchored nanoscale iron is prepared by the process comprising the steps of:

(i) cleaning the zeolite with distilled water for 3 hours; (ii) soaking the zeolite cleaned in step (i) into HNO₃ of IN for 3 days and cleaning said zeolite with degassed water;

(FeCl₃-6H O) solution whose pH is neutralized by NaOH and stirring the solution strongly for more than 10 hours; (iv) pouring out the clarified supernatant liquid of step (iii) carefully and pouring in

0.5mM NaCl solution, and maintaining the solution for 24 hours;

(v) repeating the step (iv) 5 times; and

3. The remediation method of contaminated materials by using zeolite anchored nanoscale iron according to claim 1, wherein said zeolite anchored nanoscale iron is prepared by the process comprising the steps of:

(i) cleaning zeolite with distilled water for 3 hours;

(ii) putting the zeolite cleaned in step (i) into 1.0M ferric chloride (FeCl -6H₂O) solution and infiltrating said ferric chloride (FeCl₃-6H O) solution into the inner structure of zeolite by stirring slowly for 2 hours;

(iii) inducing precipitation of Fe° as in formula (6) inside the structure of the zeolite by adding 1.6M of sodium borohydride liquid into the solution of (ii) while stirring the solution,

Fe(H₂O)₆ ^3"+ 3BH₄- + 3H₂O→Fe°| + 3B(OH)₃ + 10.5H₂ Formula (6).

4. The remediation method of contaminated materials by using zeolite anchored nanoscale iron according to claim 1 wherein said zeolite anchored nanoscale iron is prepared by the process comprising the steps of:

(i) cleaning zeolite with distilled water for 3 hours; (ii) impregnating 2g of zeolite into 500ml of ferric nitrate (Fe(NO₃)₃-9H O) solution with concentration 0.5-2M and stirring the solution for 24 hours;

(iv) repeating step (ii) and step (iii) four times; (v) drying the zeolite of step (iv) at 80 °C ; and (vi) buπiing the zeolite of step (v) at 450 ^°C .

5. A reactive wall including zeolite anchored nanoscale iron, said zeolite being prepared by the process comprising the steps of; (i) cleaning zeolite with distilled water for 3 hours;

(ii) soaking the zeolite cleaned in step (i) into HNO₃ of IN for 3 days and cleaning said zeolite with degassed water;

(FeCl₃-6H₂O) solution whose pH is neutralized by NaOH, and stirring the solution strongly for more than 10 hours;

(iv) pouring out the clarified supernatant liquid of step (iii) carefully and pouring in

0.5mM NaCl solution, and maintaining the solution for 24 hours;

(v) repeating the step (iv) 5 times; and

6. A reactive wall including zeolite anchored nanoscale iron, said zeolite being prepared by the process comprising the steps of; i) cleaning zeolite with distilled water for 3 hours;

(ii) putting the zeolite cleaned in step (i) into 1.0M ferric chloride (FeCl₃-6H₂O) solution and infiltrating said ferric chloride (FeCl₃-6H₂O) solution into the inner structure of zeolite by stirring slowly for 2 hours;

(iii) inducing the precipitation of Fe° as in formula (6) inside the structure of the zeolite by adding 1.6M of sodium borohydride liquid into the solution of (ii) while stirring the solution,

Fe(H₂O)₆ ³-+ 3BHf + 3H₂O→Fe°| + 3B(OH)₃ + 10.5H₂ Formula (6).

7. A reactive wall including zeolite anchored nanoscale iron, said zeolite being prepared by the process comprising the steps of;

(i) cleaning zeolite with distilled water for 3 hours;

(ii) impregnating 2g of zeolite into 500ml of ferric nitrate (Fe(NO₃)₃-9H₂O) solution with concentration 0.5-2M and stirring the solution for 24 hours;

(iv) repeating step (ii) and step (iii) four times; (v) drying the zeolite of step (iv) at 80 ^°C; and (vi) burning the zeolite of step (v) at 450 ^°C .

8. The remediation method of contaminated materials by using zeolite anchored nanoscale iron according to claim 1, wherein the reactive wall including zeolite anchored nanoscale iron comprises mixture of reactive material including zeolite anchored nanoscale iron, and soil with weight ratio of 5-20: 1.