KR20120016888A - A method of adsorbing and immobillizing heavy metals in contaminated soil using modified clays and phosphates - Google Patents

Abstract

PURPOSE: A method for adsorbing and immobilizing heavy metal polluted soil using modified clay and a phosphate-based compound is provided to improve the eliminating effect of heavy metals by eliminating heavy metals from polluted soil and immobilizing the heavy metals. CONSTITUTION: Heavy metals are eliminated from polluted soil by mixing modified clay and the polluted soil. The modified clay is modified with iron oxide or manganese oxide. A phosphate-based compound is further used with the modified clay. The clay is diatomate, montmorillonite, bentonite, zeolite, smectite, phyllosilicate, saponite, beidellite, nontronite, vermiculite, kaolinite, halloysite, mica, muscovite, paragonite, dickite, nacrite, halloysite, antigorite, chrysotile, hectorite, clintonite, donbassite, cookeite, silica, or the combination of the same. The phosphate-based compound is diammonium phosphate, hydroxyapatite, waste phosphoric acid, K_3PO_4, K_2PO_4, KH_2PO_4, CaHPO_4, FeH_2PO_4, FeHPO_4, AlH_2PO_4, Na_2HPO_4, NaH_2PO_4, or the combination of the same.

Description

A method of adsorbing and immobillizing heavy metals in contaminated soil using modified clays and phosphates

The present invention relates to a method for adsorbing and immobilizing heavy metal contaminated soil using modified clay and phosphate-based compounds, and more specifically, iron or manganese oxide-modified clay and phosphate-based compounds having improved heavy metal adsorption capacity to soils contaminated with heavy metals. The present invention relates to a method for treating heavy metal contaminated soil that can remove heavy metals in contaminated soil.

Soil pollution is steadily increasing due to unauthorized discharge and accidental discharge of waste oil, groundwater inflow of heavy metals from waste mines, surface water uptake by dioxin rainfall from incinerators and vehicle emissions, and leachate from landfills. I'm having a hard time.

In particular, heavy metals remain in the soil semi-permanently because of the long processing time, unlike harmful organic substances. Many heavy metals in the soil are combined with organic materials in the soil, so that they exist in low solubility and can easily move to the surrounding environment, which is adversely affected by long-term leakage in the surrounding ecosystem. Conventionally used methods for treating such heavy metal contamination in the soil include soil washing, plant purification, solidification / stabilization method. However, in the case of soil washing, secondary pollution by washing solution occurs and the processing cost is high.In the case of the plant purification method, the application of plants according to the concentration of contaminants is restricted and the plants must be removed on a regular basis. There is a disadvantage of causing ecosystem pollution, and in the case of solidification / stabilization, there is a problem that the toxicity in the soil remains. Therefore, new technology development is required to solve this problem.

On the other hand, the method of restoring using a phosphate solution in soil contaminated with heavy metals (Korean Patent No. 10-2003-0021646), selective adsorption and filtration of environmentally harmful organics, a method for producing porous crosslinked clay that can be applied as a catalyst (Korean Patent No. 10-2000-0010120), a metal ion that is harmful to the environment is converted into a new mineral phase by putting zeolites, goto-lime lime (Ca (OH) ₂ .Mg (OH) ₂ ), etc. in the soil. Method of stabilizing soil (Korean Patent No. 10-2004-0025437), Method of stabilization of heavy metal contaminated soil through the combination of a number of stabilizing agents (Korean Patent No. 10-2009-0129847), heavy metals using phosphate and ultrasonic Immobilization method (Korean Patent No. 10-2009-0127550) and the like have been reported.

In addition, a study on the purification of lead-contaminated soil and groundwater using phosphate-based glass (Cho et. Al., Journal of Korean Society for Environmental Engineering Spring Conference, 1998), Evaluation of Applicability of Liquid Phosphate Restoration Technology to Heavy Metal-Contaminated Soil ( Lee et al., Korean Journal of Waste Science, Vol. 21, No. 7, 2004), and research on restoration of lead-contaminated soil using liquid phosphate (Jang et. Al., Master's Thesis, Sangmyung University, 2004). Heavy metals in the soil chemically combine with phosphoric acid to form insoluble hydroxypyromorphite.

However, this conventional technique has a problem in that the immobilization treatment for heavy metal contaminated soil using phosphate has a long application limitation, a high treatment cost, and a long time for stable treatment, depending on the depth of the pollutant. In the case of using the adsorption treatment, most of them are limited to the treatment of air pollutants or organic pollutants such as phenol.

Therefore, the present inventors can treat and remove heavy metals with high mobility by treating iron or manganese oxide-modified clays with improved heavy metal adsorption capacity in heavy metal contaminated soils. By further treating the phosphate-based compound was confirmed that the heavy metal immobilization can be further improved the heavy metal removal effect and completed the present invention.

It is an object of the present invention to provide a method for treating heavy metal contaminated soils that can remove heavy metals from contaminated soil by treating iron or manganese oxide modified clays and phosphate-based compounds with improved heavy metal adsorption capacity on heavy metal contaminated soils. .

In order to solve the above problems, the present invention provides a method for treating heavy metal contaminated soil that can efficiently and stably remove heavy metal from soil contaminated with heavy metal.

In one embodiment, the present invention includes the step of removing the heavy metal in the contaminated soil by mixing modified clay modified with iron (Fe) oxide or manganese (Mn) oxide with improved heavy metal adsorption capacity with the soil contaminated with heavy metal. Provides a method for treating heavy metal contaminated soil.

Furthermore, the present invention can provide a method for treating heavy metal contaminated soil in which the efficiency of removing heavy metals in contaminated soil is significantly increased by further mixing and using a phosphate compound with the modified clay.

As used herein, the term "modified clay" means clay that has improved its adsorption capacity for heavy metals by modifying natural clay with a surface modifier. Specifically, modified clay expands in water, and iron (Fe), which is a metal oxide with a large surface charge, is a clay having the advantage of effectively absorbing heavy metals due to its high adsorption capacity, ion exchangeability, and high absorption, and surface area. Or by modifying it with manganese (Mn) oxide. The modified clay can maximize the adsorption efficiency of heavy metals efficiently and stably by improving the adsorption capacity for heavy metals.

In the present invention, the clay is diatomate, montmorillonite, montmorillonite, bentonite, zeolite, zemite, smectite, phyllosilicate, saponite, beydellite ), Nontronite, vermiculite, kaolinite, halloysite mica, muscovite, paragonite, dickite, nakrite (nacrite), halloysite, antigorite, chrysotile, hectorite, clintonite, donbassite, cookeite, Silica or a combination thereof may be used, but is not limited thereto.

In one embodiment of the present invention, diatomite and montmorillonite having structural differences of clay are used as the surface modifiers of iron (Fe) oxide or manganese (Mn) oxide, respectively. Diatomaceous earth is a natural clay having an amorphous amorphous structure and montmorillonite is a smectite-based natural clay having a 2: 1 plate structure.

Through the experimental example of the present invention, the modified clay as the manganese (Mn) amorphous diatomaceous earth was confirmed that the most preferable in terms of efficiency of heavy metal removal in contaminated soil.

In the present invention, the modified clay is preferably mixed with 0.1 to 10 parts by weight with respect to 100 parts by weight of contaminated soil. If the modified clay is mixed less than 0.1 parts by weight, the heavy metal removal efficiency is lowered, and even if mixed with more than 10 parts by weight heavy metal removal efficiency does not increase significantly is uneconomical.

In the present invention, the modified clay is most preferably mixed in 5 parts by weight based on 100 parts by weight of contaminated soil.

In the present invention, the phosphate-based compound is applicable if the phosphate-based compound is more than 128 mg as P / g phosphate-based compound. In the present invention, as a commercial fertilizer in consideration of the smooth supply and economical efficiency, a water-soluble phosphoric acid, a phosphorus content of more than 128 mg as P / g phosphate compound was used.

In the present invention, specifically phosphate-based compounds that can be used include diammonium phosphate, hydroxyapatite, waste phosphoric acid, K ₃ PO ₄ , K ₂ PO ₄ , KH ₂ PO ₄ , CaHPO ₄ , FeH ₂ PO ₄ , FeHPO ₄ , AlH ₂ PO ₄ , AlHPO ₄ , Na ₂ HPO ₄ , NaH ₂ PO ₄ or a combination thereof.

In one embodiment of the present invention, diammonium phosphate (DAP) was used as the phosphate compound in consideration of economical efficiency.

In the present invention, the phosphate-based compound is preferably mixed in 0.3 to 3 parts by weight based on 100 parts by weight of contaminated soil.

Through the experimental example of the present invention, it was confirmed that it is preferable to mix the phosphate-based compound in 0.3 to 3 parts by weight with respect to 100 parts by weight of contaminated soil.

Furthermore, the experimental examples of the present invention showed that when the modified clay and the phosphate-based compound were treated at the same time, they showed more stable and effective heavy metal removal efficiency than when each was treated alone.

The present invention can be removed by the adsorption treatment of heavy mobile metals by treating iron or manganese oxide-modified clay with improved heavy metal adsorption capacity in the soil contaminated with heavy metals, and at the same time by further treating the phosphate-based compound to fix the heavy metals There is an effect that can provide a method for treating heavy metal contaminated soil that can further improve the heavy metal removal effect.

1 is a SEM analysis showing the surface morphology change before and after the modification of montmorillonite. (A) is Montmorillonite before modification, (b) is Fe-Montmorillonite, and (c) is Mn-Montmorillonite.
Figure 2 is a SEM analysis showing the surface change before and after the modification of the diatomaceous earth. (A) is Diatomite before modification, (b) is Fe-Diatomite, and (c) is Mn-Diatomite.
Figure 3 shows the results of Pb adsorption on the modified clay of montmorillonite.
Figure 4 shows the results of Pb adsorption on modified clay of diatomaceous earth.
5 shows the results of Pb immobilization using phosphate (DAP).
FIG. 6 is a graph showing the results of elution experiments after heavy metal adsorption and immobilization on samples mixed with modified clay Mn-Diatomite and phosphate (DAP). In this case, (a) is 0.0039 g of DAP, (b) is 0.0077 g of DAP, (c) is 0.0155 g of DAP, and (d) is 0.0310 g of DAP, respectively. In addition, Fraction 1 (exchangeable) is the most important step for the adsorption by cation exchange, the mobility and bioavailability of heavy metals, Fraction 2 (carbonate) for the formation of Me (CO ₃ ) by binding to inorganic carbon The heavy metal in Fraction 2 is the precipitated state combined with carbonate, and Fraction 3 (reducible) refers to the binding of metal oxide (Iron, manganese oxide). Heavy metal is present in the crystalline lattice of mineral. Mobility is inferior, and Fraction 4 (organic material) refers to the part combined with biomass and humic substance in soil, and Fraction 5 (residual) refers to the state combined with phosphate, sulfur, hydroxide, etc. in soil. do.
FIG. 7 shows the results of XRD analysis of Pb-contaminated soils after adsorption and immobilization of Pb-contaminated soils using modified clays Mn-Diatomite and phosphate (DAP).

Hereinafter, the configuration and effects of the present invention will be described in more detail with reference to examples, but these examples are merely illustrative of the present invention, and the scope of the present invention is not limited only to these examples.

Example 1 Preparation of Montmorillonite Modified with Iron Oxide

First, 15 g of montmorillonite was added to 400 ml of a mixed solution of FeCl ₃ (7.8 g / L, 28 mmol / L) and FeSO ₄ (3.9 g / L, 14 mmol / L), and NaOH (100 ml, 5 M) was supplied. The formation of iron oxide was induced. At this time, each of the particles of iron oxide (Iron oxide) was stirred so as to be independently synthesized, and sodium hydroxide (NaOH) was supplied at a slow rate (0.8 ml / min) so that the reaction proceeded sufficiently. The prepared Fe-Montmorillonite is an amount corresponding to 1: 1 by weight ratio of Montmorillonite / Iron oxide, Fe-Montmorillonite was sufficiently oxidized in air, dried at 60 ℃ and stored in a glass bottle was used.

Example 2: Preparation of Montmorillonite Modified with Manganese Oxide

MnCl ₂ (5.6 g / L, 28 mmol / L) and MnSO ₄ (2.4 g / L, 14 mmol / L) instead of FeCl ₃ and FeSO ₄ as surface modifiers in the same manner as in Example 1 Montmorillonite was prepared.

Example 3: Preparation of Diatomaceous Earth Modified with Iron Oxide

Fe-Diatomite was prepared in the same manner as in Example 1, except that diatomaceous earth was used instead of montmorillonite as natural clay.

Example 4 Preparation of Diatomite Modified with Manganese Oxide

MnCl ₂ (5.6 g / L, 28 mmol / L) and MnSO ₄ (2.4 g / L, 14 mmol / L) instead of FeCl ₃ and FeSO ₄ as surface modifiers in the same manner as in Example 1 -Diatomite was prepared.

Preparation Example 1 Preparation of Heavy Metal Contaminated Soil

PbNO ₃ (Aldrich Chemical Co,> 98%) 1500ppm in 50g of natural soil was artificially contaminated at 200rpm at 25 ℃ for 3 days to prepare a Pb artificial soil.

Experimental Example 1: Investigation of surface morphology of modified clay

In order to investigate the morphological changes of the surface of montmorillonite and diatomaceous earth before the modification and the surface of the modified clays modified as in Examples 1 to 4, the surfaces of natural clays and modified clays were examined using a scanning electron microscope (SEM). It was.

As a result, the surface shape change before and after the modification of montmorillonite is shown in Figure 1, the surface change before and after the modification of the diatomaceous earth is shown in Figure 2. In Figure 1 (a) is Montmorillonite before reforming, (b) is Fe-Montmorillonite, (c) is Mn-Montmorillonite, in Figure 2 (a) is Diatomite before reforming, (b) is Fe-Diatomite, (c) Is Mn-Diatomite.

1 and 2, it was confirmed that the surface area of montmorillonite and diatomaceous earth was wider due to the formation of oxide after modification.

Experimental Example 2: Measurement of Heavy Metal Adsorption Efficiency Using Modified Clay

Heavy metal adsorption efficiency was measured in the aqueous heavy metal solution using the modified clay prepared in Examples 1 to 4.

Specifically, 1 g of Pb-contaminated soil prepared in Preparation Example 1 contained Fe-Montmorillonite, Mn-Montmorillonite, Fe-Diatomite, and Mn-Diatomite, which were prepared in Examples 1 to 4, in each 50 ml vial. After homogeneously mixing, a pH buffer solution prepared using MES ((2-N-Morpholino) Ethanesulphonic Acid) buffer was injected so that the water content was 50%, and the heavy metals were immobilized. After the immobilization experiment, the sample was centrifuged (2,000 rpm, 20 min), and then separated with a 0.2 μm cellulose nitrate membrane filter (Whatman). Concentration was measured using an Atomic Absorption Spectrometer (AAS).

3 to 4 show Pb adsorption results for modified clay of montmorillonite and diatomaceous earth, respectively.

3 to 4, it was confirmed that the amount of heavy metal adsorption increased significantly in the modified clay modified with iron oxide or manganese oxide compared to natural clay.

Meanwhile, Table 1 shows the maximum adsorption amounts of heavy metals of montmorillonite and diatomite before and after reforming.

Maximum adsorption amount of Pb in modified clay Max adsorption amount Diatomaceous earth Fe-
diatomite Mn-
diatomite Montmorillonite Fe-
montmorillonite Mn-
montmorillonite mmol / g 0.0248 0.45 1.07 0.233 0.329 0.178 mg / g 5.13 93.2 221.69 47.67 68.17 148.76

As can be seen in Table 1, the maximum adsorption amount of Montmorillonite (Diatomite) and diatomite (Diatomite) after the modification with Fe and Mn is about three times or more in the case of Montmorillonite (Montmorillonite) modified with Mn based on mg / g, Diatomite has been improved by about 40 times or more, and it has been improved by about 18 times in the case of montmorillonite modified with Fe and about 1.4 times in the case of diatomite.

Experimental Example 3: Measurement of Heavy Metal Immobilization Efficiency Using Phosphate Compound

The heavy metal immobilization efficiency was measured in a heavy metal aqueous solution using diammonium phosphate (DAP) as a phosphate compound.

Specifically, DAP (Diammonium phosphate) in 1 g of the soil contaminated with heavy metals prepared in Preparation Example 1 was added to 50 ml vial for each concentration, as shown in Table 2, and immobilized in a tumbler (20 ° C., 10 rpm) for 24 hours. I was. At this time, MES ((2-N-Morpholino) Ethanesulphonic Acid) buffer solution was injected to have a water content of 50%. After the immobilization experiment, the sample was centrifuged (2,000 rpm, 20 min), and then separated with a 0.2 μm cellulose nitrate membrane filter (Whatman). Concentration was measured using an Atomic Absorption Spectrometer (AAS).

Classification (DAP mmol) Heavy metal contaminated soil (g) DAP (g) 0 One 0 16 One 0.0039 32 0.0077 64 0.0155 128 0.0310

5 shows the results of Pb immobilization using phosphate (DAP).

5, when the phosphate treatment was confirmed that lead (Pb) is a heavy metal is increased heavy metal elution from the soil sample.

Experimental Example 4: Measurement of Heavy Metal Adsorption and Immobilization Complex Efficiency Using Modified Clay and Phosphate Compound

Heavy metal adsorption and immobilization efficiency in heavy metal aqueous solution was measured using diammonium phosphate (DAP) as the modified clay and the phosphate compound prepared in Examples 1 to 4.

As shown in Table 3, the modified clay Mn-Diatomite and DAP (Diammonium phosphate), which were shown to have the best adsorption capacity in Experimental Example 2 as modified clay in heavy metal contaminated soil, were contained in each 50ml vial, and were the same as those of Experimental Examples 2 and 3. The dissolution experiment was performed after heavy metal adsorption and immobilization experiments.

division Heavy metal contaminated soil (g) Mn-Diatomite (g) DAP (g) (a) One 0.05 0.0039 (b) 0.0077 (c) 0.0155 (d) 0.0310

FIG. 6 is a graph showing the results of elution experiments after heavy metal adsorption and immobilization on samples mixed with modified clay Mn-Diatomite and phosphate (DAP). As can be seen in FIG. 6, when mixed clay and phosphate (DAP) were mixed and mixed, heavy metal adsorption using only modified clay and heavy metal immobilization treatment using only phosphate (DAP) during heavy metal dissolution showed stable and effective heavy metal treatment efficiency. And it was found.

In addition, Figure 7 shows the results of XRD analysis on Pb contaminated soil after the adsorption and immobilization of Pb contaminated soil using Mn-Diatomite and phosphate (DAP) modified clay. 7, it can be confirmed that even in the adsorption and immobilization treatment using modified clay and phosphate on heavy metal contaminated soil, insoluble hydroxypyromorphite is formed, as in the immobilization treatment using only phosphate, and stable treatment of heavy metals is possible.

Therefore, in view of the above experimental results, heavy metal treatment using modified clay and phosphate-based compound including iron oxide or manganese oxide prepared in Examples 1 to 4 according to the present invention is a heavy metal adsorption or phosphate-based compound using only modified clay. It can be seen that it is more stable and efficient for the treatment of heavy metals in contaminated soil by using a combination of modified clay and phosphate compound than the heavy metal immobilization efficiency using only bay.

Claims (10)

A method of treating heavy metal contaminated soil, comprising: mixing modified clay modified with iron (Fe) oxide or manganese (Mn) oxide with soil contaminated with heavy metal to remove heavy metal in the contaminated soil.
The method for treating heavy metal contaminated soil according to claim 1, further comprising a phosphate compound in combination with the modified clay.
The clay according to claim 1, wherein the clay is diatomate, montmorillonite, bentonite, zeolite, smectite, phyllosilicate, saponite, and saponite. beidellite, nontronite, vermiculite, kaolinite, halloysite mica, muscovite, paragonite, dickite, nak Nacrite, halloysite, anticorite, chrysotile, hectorite, clintonite, donbassite, cookeite A method of treating heavy metal contaminated soil, which is silica or a combination thereof.
The method of claim 1, wherein the clay is diatomaceous earth or montmorillonite.
The method of claim 1, wherein the modified clay is diatomaceous earth modified with manganese (Mn).
The method of claim 1, wherein the modified clay is mixed with 0.1 to 10 parts by weight with respect to 100 parts by weight of contaminated soil.
The method of claim 6, wherein the modified clay is mixed in 5 parts by weight with respect to 100 parts by weight of contaminated soil.
The method of claim 1, wherein the phosphate compound is a phosphate compound that is greater than or equal to 128 mg as P / g phosphate compound.
The method of claim 8, wherein the phosphate compound is diammonium phosphate, hydroxyapatite, waste phosphoric acid, K ₃ PO ₄ , K ₂ PO ₄ , KH ₂ PO ₄ , CaHPO ₄ , FeH ₂ PO ₄ , FeHPO ₄ , AlH ₂ A method of treating heavy metal contaminated soil, which is PO ₄ , AlHPO ₄ , Na ₂ HPO ₄ , NaH ₂ PO _4, or a combination thereof.
The method of claim 1, wherein the phosphate compound is mixed in an amount of 0.3 to 3 parts by weight based on 100 parts by weight of the contaminated soil.

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