KR20110096350A - Remediation method for heavy metal contaminated soil - Google Patents

Abstract

PURPOSE: A method for restoring soil contaminated with heavy metal is provided to improve the efficiency of a magnetic force-based separating process by implementing a soil aggregate dispersing process before the magnetic force-based separating process. CONSTITUTION: Soil contaminated with heavy metal is collected(10). Soil aggregates of the soil are dispersed into a plurality of separated soil particles by introducing the soil into a dispersing solution to release the cohesion of the soil(20). Suspension with the soil particles and the dispersing solution passes through magnetic field to separate the soil particles based on magnetic force(40). The soil particles are classified using a sieve by the sizes of the particles between the dispersing process and the magnetic force-based separating process(30).

Description

Remediation method for heavy metal contaminated soil}

The present invention relates to a method for restoring contaminated soil, and more particularly, to a method for restoring heavy metal contaminated soil for restoring the soil by removing heavy metal from soil contaminated with heavy metals such as arsenic, cadmium, and lead.

Soil pollution occurs through a variety of routes, including waste dumping, hazardous material leaks, pesticide and fertilizer use, and incineration. Soil pollution not only causes various problems such as disruption of soil ecosystem, pollution of crops and human absorption of pollutants, but also acts as a source of pollution that causes secondary pollution of surface water, groundwater and air. Soil pollution is more chronic than air and water pollution and takes much time and money to recover.

Recognizing the seriousness of the adverse effects of soil pollution on humans and ecosystems, Korea has enacted and implemented the Soil Environment Conservation Act. The Soil Conservation appointed pollution reference value for 16 items (Cd, Cu, As, Hg , Pb, Cr 6 +, Zn, Ni, F, of the compound, CN, BTEX, TPH, TCE , PCE organic) administration Doing.

In particular, heavy metals among soil pollutants can cause fatal diseases such as Minamata, Itai-tai, and cancer. Therefore, not only pollution should be prevented in advance, but damage by heavy metals should be reduced by restoring the soil that has already been contaminated. .

Recently, restoration projects for heavy metal contaminated soils have been actively carried out. Soil cleaning, electrokinetic extraction, stabilization, phytoremediation, and landfill blocking are commonly applied to clean heavy metal contaminated soil.

In Korea, the soil washing method has been commercialized and used a lot in the field, and the stabilization method and the electrokinetic extraction method are operated only at the pilot scale. Soil cleaning and galvanic extraction techniques have exposed many limitations to the purification of contaminated soils with high clay and iron oxide contents. When the soil washing method is applied to polluted soils with high clay content, there is a limit in economic efficiency and low heavy metal extraction efficiency due to the large amount of washing solution to be added per unit soil. In addition, according to the continuous extraction method that continuously extracts heavy metals while increasing the strength of extraction power, they are classified into iron oxide form and residual form (residual fraction, which should be extracted as aqua regia as the last step of continuous extraction). There are heavy metals (PbO, CuO, etc.), and when the soil washing method is applied to soils with a high content of heavy metals, it is impossible to extract them with general cleaning solution (weak acid solution) and use very strong acid. have. That is, there is a problem in that a large amount of strong acid should be used directly in the soil contaminated with heavy metals.

On the other hand, the landfill blocking method is used when it is difficult to purify the contaminated soil with the existing commercial method, and the use case is very small at high cost. Phytoremediation is economical but takes a long time to purify and is used in addition to other physicochemical methods.

Galvanic extraction is a method of extracting pollutants from the heavy metals contained in the soil using direct current. Galvanic extraction method extracts mainly from water-soluble heavy metals from contaminated soil and shows high extraction efficiency only by maintaining water content above a certain level. Some sites use the weak acidic heavy metal leaching solution to apply the process, but there are limitations in heavy metal leaching, so it is only applicable to limited sites.

In addition, in Korea, a lot of stabilization methods are applied to reduce the toxicity, solubility, and mobility of heavy metals by adding adsorbents and precipitants to the soil contaminated with heavy metals, and lime and steel slag are widely used as stabilizers. Lime and steel slag injected into the soil can raise the soil pH and convert the highly soluble heavy metal into the form of hydroxide or carbonate.However, the stabilization method also requires long-term restoration of soil due to the continuous acid rain and the short useful life of the neutralizer. You cannot guarantee the effect.

Table 1 and Figure 1 below shows the results of the literature survey on the content ratio of Cu, Zn, Pb, Cd, Ni, Cr, As by presence type in 177 contaminated soils.

division receptivity
( water soluble Of
exchangeable )
lead carbonate
( Carbonate )
Iron oxide, manganese oxide
( Fe , Mn - oxide )
Organic matter
( Organic )
Residue
( Residual ) --------------------------% ----------------------- --- CD 25.8 (24.3) 16.7 (13.1) 15.8 (14.0) 15.0 (11.4) 32.9 (27.9) Cu 9.6 (15.2) 10.1 (11.1) 21.4 (17.8) 21.7 (17.8) 44.4 (28.0) Pb 12.2 (17.9) 16.0 (16.9) 19.1 (17.7) 13.7 (10.5) 43.4 (31.7) As 4.7 (6.6) 11.2 (14.7) 35.3 (22.3) 6.4 (6.1) 43.4 (31.1) Cr 1.2 (1.7) 1.2 (1.7) 9.1 (8.6) 10.2 (12.6) 82.4 (17.1) Zn 12.0 (19.4) 9.8 (8.2) 23.5 (18.1) 12.5 (12.3) 45.8 (28.5) Ni 6.8 (8.9) 4.1 (3.1) 12.1 (7.7) 11.9 (10.4) 71.8 (17.3)

[Heavy metal content table by existence type. () Is the standard deviation]

Referring to Table 1 and Figure 1, it was found that more than 50% of the iron oxide and manganese oxide, the remaining form of the presence of heavy metals present in the soil. The content ratio of heavy metals in the soil by soil type is the main data for predicting heavy metal behavior and toxicity, selecting and applying restoration methods, and monitoring.

That is, the higher the content of water soluble, exchangeable and carbonate forms, the higher the toxicity and mobility of heavy metals. This means that the restoration target can be easily achieved by applying soil washing and electrokinetic extraction methods. However, soils with high levels of heavy metals such as iron oxides, manganese oxides, and residual forms are not easy to apply in soil washing or electrokinetic extraction methods, which means that very strong extraction solutions can be used to achieve restoration goals. do. For example, the weak acid cleaning solution (<0.1NH ⁺ ), which is most commonly used in soil washing, can extract water-soluble, carbonate and amorphous iron oxide and manganese oxide heavy metals from the soil, And heavy metals in residual form are difficult to extract.

Therefore, in order to overcome the limitations of the existing methods and achieve smooth restoration goals, it is necessary to develop and apply a new concept method that can effectively remove heavy metals in the form of iron oxide, manganese oxide and residual forms.

The present invention is to achieve the above object, a heavy metal soil pollution restoration method that can be treated separately after separating heavy metals, particularly iron oxide, manganese oxide form and residual form heavy metal contained in the soil from the soil by magnetic force The purpose is to provide.

Heavy metal soil pollution restoration method according to the present invention for achieving the above object is a collection step of collecting soil contaminated with heavy metal, by putting the collected soil in a dispersion to release the cohesion between a plurality of soil particles independent A dispersion step of dispersing into a plurality of soil particles and a magnetic separation step of separating the soil particles by a magnetic through a magnetic field through the suspension is mixed with the soil particles and dispersion.

According to one embodiment of the present invention, between the dispersing step and the magnetic separation step, it may further comprise a particle size selection step of screening the soil particles by sifting the suspension into a network that can pass only particles of a predetermined particle size or less. have.

In addition, according to an embodiment of the present invention, in the magnetic separation step, the suspension is passed through the steel wool in a state in which power is applied to the electromagnet after interposing the steel wool, the wires are agglomerated between the electromagnets facing each other Magnetic particles in the suspension are attached to the steel wool, and after the suspension has passed through the steel wool, it is attached to the steel wool by releasing the power of the electromagnet and spraying a flushing liquid onto the steel wool. Collect soil particles in the flushing liquid.

In addition, in one embodiment of the present invention after performing the first solid-liquid separation step of collecting the soil particles from the flushing liquid by solid-liquid separation of the flushing liquid containing the soil particles having a magnetic force after the magnetic separation step, continuously from the magnetic soil particles A heavy metal removal step is performed to extract and remove heavy metals.

In addition, in one embodiment of the present invention, an alkaline solution, in particular, a phosphate solution may be used as the dispersion used in the dispersing step, and in another embodiment, an anionic surfactant may be used.

In the conventional soil washing method, electrokinetic extraction method, and stabilization method, iron oxide, manganese oxide heavy metals and residual heavy metals were not easily removed from the present forms of heavy metals. It is possible to easily separate heavy metals in difficult-to-remove form from the soil.

In the present invention, since the treatment is performed on the soil containing a large amount of heavy metal separated by magnetic separation, there is an advantage that it is economical and effective than the direct treatment on the entire soil to be treated.

In addition, the present invention has a great advantage that the magnetic separation can be effectively performed by going through the dispersion step prior to the magnetic separation.

In addition, secondary pollution, which is always a problem in the environmental pollution treatment technology, that is, the treatment problem for the chemicals used for treatment does not occur in the present invention has the advantage that it is very environmentally friendly. That is, since the dispersion used in the present invention is recycled again, there is an advantage that the problem of secondary treatment does not occur.

1 is a graph showing the content of heavy metals according to the type of classification according to the classification used in the heavy metal continuous extraction method.
2 is a schematic flowchart of a heavy metal contaminated soil restoration method according to an embodiment of the present invention.
3 is a schematic diagram of soil intrusion.
4 is an electron micrograph of soil incidence.
5 is a photograph in which iron oxide is deposited on the silicate surface.
6 is a photograph of soil flakes.
7 is a view schematically showing the structure of a diffusion double layer.
8 to 11 are graphs showing the results of experiments on the dispersion effect of the dispersion.
12 is a schematic configuration diagram of a magnetic separator used in the magnetic separation step.
13 to 16 are graphs of the correlation between the concentrations of heavy metals extracted from aqua regia and the large susceptibility of the soil.
17 is a result table of the heavy metal removal efficiency of the heavy metal contaminated soil restoration method according to an embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings, it will be described in more detail with respect to the heavy metal contaminated soil restoration method according to an embodiment of the present invention.

2 is a schematic flowchart of a heavy metal contaminated soil restoration method according to an embodiment of the present invention.

2, the heavy metal contaminated soil restoration method 100 according to a preferred embodiment of the present invention is a collection step 10, dispersion step 20, particle size selection step 30, magnetic separation step 40, 1,2 solid-liquid separation step (50, 60) and heavy metal removal step (70).

In the collecting step 10, the heavy metal contaminated soil to be treated is excavated and collected. This heavy metal contaminated soil varies in major pollutants depending on the collection sites such as plating factories and mining related factories, and contains a large amount of heavy metals such as arsenic, lead, cadmium and chromium. After collecting the contaminated soil, the crushing of the contaminated soil is performed before the dispersion step 20 is performed.

In the dispersing step 20, the collected contaminated soil is added to the dispersion, so that the soil particles aggregate to each other to separate the soil existing in the form of soil incidence into a plurality of soil particles.

Soil is composed of about 50% minerals and organic matter, and about 50% gas and moisture. As shown in the schematic diagram of FIG. 3 and the electron micrograph of FIG. 4, most soils except sand soil are composed of several particles. It exists in the form of an aggregate. Soil intrusion is formed by the cohesion of the moire and silt particles by coagulation of organic matter, clay, iron oxide, and manganese oxide. Iron oxide and manganese oxide are mainly composed of secondary minerals produced during the weathering process of silicates, primary minerals. Therefore, the iron oxide and manganese oxide produced during the weathering process, as shown in the photographs of FIGS. 5 and 6, is precipitated on the surface of the silt-sand particles or precipitated between the particles to promote granulation. That is, in FIG. 5, a small size of iron oxide is precipitated on the silicate surface, and fine iron oxide particles, which are shown in red in FIG. 6, are dispersed throughout the soil inlet and perform aggregation.

As will be described later, in the magnetic separation step 40, the soil particles are separated from the magnetic particles and the non-magnetic particles. For effective magnetic separation, the soil particles are separated as much as possible, so that the soil particles do not aggregate and exist as independent individual particles. For example, iron oxide, which is a magnetic substance, is deposited on the surface of silicate, which is a nonmagnetic substance, and thus magnetic separation cannot be performed without separating them from each other. In the dispersion step 20, the soil particles are individually present using the dispersion as a pretreatment of the magnetic separation.

Here, the soil particles are used as a generic term for all the particles that form the soil, such as sand, silt, clay, iron oxide, manganese oxide, organic matter, heavy metals, and magnetic particles and non-magnetic particles can be separated according to the magnetic properties. Note that it is used as a terminology.

As described above, the success of the magnetic separation depends on the degree of dispersion of the particles in the dispersion. In other words, minerals containing heavy metal precipitated on the surface of coarse particles or coagulated at the soil inlet should be present as individual particles.

Soil dispersion and flocculation are determined by the surface charge of the soil particles and the chemical properties of the aqueous solution. The surface charges of soil particles are classified into permanent charges derived from the mineral crystal structure and variable charges determined by the surrounding physicochemical environment. The soil particle surface shows both permanent and variable charges, or only permanent or variable charges.

Clay minerals have a layered structure, which shows permanent negative charges on the (001) plane (each layer in the layered structure), which is the concept of crystallography, and variable charges on the broken edges. On the other hand, the surface of iron oxide mineral, manganese oxide mineral and organic material exhibits variable charge whose charge varies depending on the pH of the surrounding solution and the type of ions.

In general, the soil has a relatively high content of minerals representing permanent negative charge, so the total surface charge of the soil is negative. Iron oxides and manganese oxides have a positive charge on the soil with a point of zero charge (PZC), that is, a pH of 7-9 with zero surface charge. Iron oxide and manganese oxide having surface charges and fine particle sizes aggregate the clay minerals and organic matters having surface negative charges through bridging of electrostatic forces.

Thus, the dispersion of soil particles is possible by the charge control of the particle surface. When the electric charges of soil particles such as iron oxide and manganese oxide having variable surface charges are converted to negative charges, almost the surface of the soil particles is negatively charged, so that the soil particles are dispersed by repulsion between the particles.

In order to stand out a soil particle surface with a variable charge-negative charge to increase the pH of the dispersion to more than PZC of the soil particles, or on the soil surface of the particles of phosphate (phosphate, PO ₄ ^{3 -)} a strong surface attraction force, such as a number (approaching It can be achieved through the adsorption of negative ions having a multi-charge.

Thus, in one embodiment of the present invention, an alkaline solution is used as a dispersion. The pH of this alkaline solution is in the range of 8-12. The various particles in the soil generally have a surface charge of zero when the pH of the environment is 7-9, and at least pH 8 or more so that the soil particles can be dispersed to a desired degree, and more preferably pH9 or more. Do. In addition, as the pH increases, the dispersing effect increases, but when the pH exceeds 12, there is almost no increase in the dispersing effect, thereby increasing only the manufacturing cost of the dispersion.

In the alkaline solution, a phosphate solution is more preferable. This is because phosphate solution has strong surface adsorption and has -trivalent charge, which can increase the repulsive force.

Meanwhile, in another embodiment of the present invention, an aqueous surfactant solution may be used as the dispersion. That is, the surfactant is composed of hydrophilic and hydrophobic parts, and the hydrophobic part is adsorbed to the soil particles and the hydrophilic part faces the opposite side (dispersion liquid). In particular, when a surfactant having an anionic hydrophilic portion is adsorbed to the soil particles, the hydrophilic portion having an anion faces the opposite side (dispersion liquid) of the soil particles. That is, the adsorption of the anionic surfactant causes the soil particles to have a larger anion, and the long, anionic, hydrophilic portion has a shape surrounding the outside of the soil particles. Therefore, in the anionic surfactant solution, soil particles become more repulsive and disperse with each other. Thus, one embodiment of the present invention uses an alkaline anionic surfactant. The pH of the aqueous surfactant solution is set in the range of pH 8-12 in the same kind of phosphate solution.

So far, dispersion conditions are alkaline (raising the soil's ambient pH), strong anions (adsorbed on soil particles to give a negative charge as a whole), or anionic surfactants (attached to soil particles to give a negative charge as a whole) Explained that it is required. As a dispersion which satisfies these conditions optimally, it may be an alkaline phosphate solution or an alkaline anionic surfactant.

As described above, even in the case of using a strong adsorbing anion (phosphate solution) or an anionic surfactant, which is a dispersant that satisfies the optimum dispersing conditions, as a dispersion, the type (discharge, size, ratio) of dissolved ions in the dispersion and the concentration of the dispersion By adjusting the soil particles can be controlled to the degree of dispersion. That is, soil particles having surface charges are adsorbed by the dissolved ions of the dispersions having opposite charges such that the total charge of the surface becomes zero in the dispersions, depending on the charge, size and concentration of the ions. The structure of the layer is determined. The structure of the adsorption layer can be described as a diffuse double layer shown in FIG. 7, wherein the thickness of the adsorption layer becomes thicker as the charge and concentration of dissolved ions in the dispersion are lower.

The thickness of the diffusion double layer (1 / κ) is expressed by the following equation.

κ ² = 8πz _i ² e ² n _i ² / εkT

1 / κ = thickness of double layer, z _i = charge of ion (i), e = electronic charge, n _i = concentration of ion (i ) in bulk solution), ε = dielectric constant of solution, k = Boltzman constant, T = absolute temperature (K).

When the thickness of the adsorption layer is thick, the soil particles are easily dispersed in the dispersion, but when the thickness of the adsorption layer is thin, they easily aggregate. Multi-charge cations Ca ^{2 +} and Mg ²⁺ in the soil are smaller in thickness than the double ⁺ layer and do not favor dispersion because they tend to aggregate negatively charged particles through bridging. Dispersion and aggregation characteristics of soil particles are expressed as sodium adsorption ratio (SAR), which is the ratio of monovalent and divalent ions.

Sodium adsorption ratio (SAR) = (Na ⁺ ) / [(Ca ^{2 +} + Mg ^{2 +} ) / 2] ^0.5

In other words, when the concentration of dissolved ions in the dispersion is the same, the higher the SAR value, the higher the soil particles exhibit the dispersion characteristics.

An example is demonstrated. The phosphate solution includes sodium phosphate containing sodium (Na), a monovalent cation, calcium phosphate or magnesium phosphate, including calcium (Ca) or magnesium (Mg), which is a divalent cation. The cations such as sodium, calcium, and magnesium contained in the phosphate are also adsorbed on the soil particles. The sodium and divalent cations of sodium, which are monovalent cations, have a greater thickness and SAR than the double layers of magnesium. Therefore, phosphate containing sodium, which is a monovalent cation, is preferable for soil dispersion.

In the phosphate solution used as a dispersion, sodium phosphate is advantageous for the dispersion of soil particles. Similarly, in the surfactant, sodium dodecyl sulfate (SDS) containing sodium can provide optimum dispersion conditions.

The dispersing effect of aqueous sodium phosphate solution and surfactant SDS solution was evaluated to be used as an optimum dispersion.

Dispersion (aqueous solution) using three phosphates of sodium orthophosphate, sodium hexametaphosphate, and sodium pyrophophate and anionic surfactant sodium dodecyl sulfate as a dispersant ) Was prepared. The dispersion was prepared by adjusting the concentration of the dispersant to 0-200 mM and the pH of 7-12. Soils were collected from Ulsan and Samcheok respectively. 1 L of dispersion and 50 g of soil were stirred for 5 minutes using a soy mixer, and then placed in a 1.5 L measuring cylinder and clay, silt, using a hydrometer in a constant temperature (25 ° C.) water bath. ), The content of sand (sand) was measured. In this experiment, it was determined that the soil was effectively dispersed when the clay content was high. In other words, when the soil intrusion is separated, it is separated into individual clays, silts, sand particles, etc., because the increase in the clay particles in the suspension can be judged that a lot of byproducts of the soil infiltration were made.

The clay content in each dispersion solution is shown in FIGS. 8 to 11.

8 and 9 is a graph showing the results of experiments in the soil of Ulsan, Figure 10 and 11 Samcheok soil, Figures 8 and 10 shows the change in the content of clay according to the concentration change of the dispersant and Figure 9 And Figure 11 shows the change in the clay content according to the pH change of the dispersion.

Referring to the experimental results, Na-hexametaphosphate and Na-pyrophosphate showed similar dispersibility in phosphate solution, but Na-orthophosphate showed relatively low dispersibility. In addition, anionic surfactant SDS showed similar dispersibility to Na-hexametaphosphate and Na-pyrophosphate.

Regarding the dispersing effect according to pH, as described above, satisfactory results were obtained at pH 8-12 or pH 9-12, and particularly, pH 11 was found to provide the optimum dispersing condition for all dispersants.

Sodium hexametaphosphate and sodium pyrophosphate showed a sharp increase in clay content at concentrations of 5 mM and a slight change in clay content above 50 mM. The phosphate solution was able to obtain a satisfactory dispersion efficiency at a concentration of 5 ~ 50mM, in particular it was confirmed to provide the optimum dispersion conditions at 10mM. In the case of aqueous surfactant solution, the concentration was rapidly increased at the concentration of 10 mM and the change of clay content was insignificant when the concentration was over 80 mM. Optimal concentration conditions were found to be 50 mM.

As described above, in the dispersing step 20, the soil is added to the phosphate solution or the surfactant solution and stirred to separate the soil morphology into individual soil particles. That is, in the state where sand and silt are aggregated by the coagulation action of iron oxide, manganese oxide, organic matter, etc., the surface charges of the soil particles are converted into negative charges so that the repulsive force acts between the soil particles. Are separated and become independent. Thus, the soil particles are separated to form a condition that can be separated from the magnetic body and the non-magnetic material in the magnetic separation to be described later.

When the dispersion step 20 is completed, the particle size selection step 30 is performed. The particle size selection step 30 sifts the suspension in which the soil particles and the dispersion are mixed into a net sieve and selects only particles having a predetermined particle size or less among the soil particles. The mesh uses standard meshes through which particles of 50-125 μm can pass. In the soil, sand is 2 to 0.074 mm in size, 0.074 to 0.002 mm in silt, 0.074 mm (74 μm) in silt, and 2 μm in clay. Iron oxides, heavy metal hydroxides, heavy metal oxides, and heavy metal sulfates, which contain a lot of heavy metals as paramagnetic minerals in soil particles, are clay and fine silt. It tends to have a particle size in between. In addition, most heavy metals in the soil tend to be present in clay and silt particles.

In an embodiment of the present invention, a non-magnetic material, sand and silt, which occupies a large proportion in soil using a 63 μm mesh, is selected from the suspension.

Herein, the size of the mesh may be defined as a mesh, but in this embodiment, the specification of the aperture opening specified by the American National Standards Institute (ASTM) is defined.

As described above, when the suspension is sieved, the coarse particles are caught in the mesh, and these coarse soil particles are mostly sand, which does not contain heavy metals, and thus can be immediately recycled into the soil without additional treatment. However, for the sake of safety, it is desirable to inspect the coarse soil particles containing heavy metals above the environmental standard and recycle them. If the heavy metals in the coarse soil particles filtered out of the sieve exceed environmental standards, separate heavy metal treatment is required.

In the particle size selection step 30, the soil particles having passed through the net in the suspension are separated into magnetic bodies and non-magnetic bodies through magnetic separation. That is, in the magnetic separation step 40, the suspension passed through the net is separated according to the magnet using the magnetic separator shown in FIG.

Referring to FIG. 12, the magnetic separator has disc-shaped electromagnets disposed to face each other, and steel wool is interposed between the electromagnets. Steel wool is made of wires entangled together, the steel wool is magnetized when power is applied to the electromagnet. Steel wool also acts as a flow path through the suspension. The steel wool is connected with a pipeline for supplying a suspension and a pipeline for supplying a flushing liquid, and a valve is attached to each pipeline. In addition, two discharge pipes are connected to the outlet side of the steel wool so that the magnetic particles and the non-magnetic particles can be discharged separately from each other, and a valve is coupled to each discharge pipe.

When power is applied to the electromagnet, a magnetic field is formed between the electromagnets and the steel wool of the steel material is magnetized. In this state, the valve of the suspension supply pipe is opened to feed the suspension into the steel wool, and the suspension passes through the steel wool, and the magnetic particles adhere to the steel wool, and the nonmagnetic particles pass through the steel wool together with the suspension and are discharged to the nonmagnetic discharge pipe. do. In this state, the valve of the magnetic particle discharge pipe is closed.

After all the suspension has passed through the steel wool, close the valve on the non-magnetic particle outlet and de-energize the electromagnet. When the power of the electromagnet is released, the magnetic field between the electromagnets is released so that the magnetic particles lose their adhesion to the steel wool. In this state, when the valve of the magnetic particle discharge pipe is opened and the flushing liquid is supplied to the steel wool, the magnetic particles pass through the steel wool together with the flushing liquid and are discharged and collected into the magnetic particle discharge pipe.

Although the electromagnet is set to 12,000 gauss in this embodiment, the strength of the magnet may vary according to the embodiment. In addition, for convenience of explanation, it is divided into magnetic particles and nonmagnetic particles, but this distinction is relative. That is, when the strength of the magnet is very weak, only ferrite magnetic magnetite is separated into the magnetic particles, while other soil particles may be separated into non-magnetic particles. Except for diamagnetic, paramagnetic soil particles can be attached to steel wool and separated into magnetic particles.

Therefore, the magnetic material and nonmagnetic material used in the present specification should be understood as a relative concept depending on whether the magnetic separator is separated according to the strength of the magnetic field.

For reference, the mass ratio of mineral particles constituting the soil is shown in the table below. The table below summarizes the magnetic properties of soil minerals and heavy metal compounds.

Soil particle
Mineral
Large autonomy
* 10 ^-8 (m ³ / kg)
Sleeping
Soil particle
Mineral
Large autonomy
* 10 ^-8 (m ³ / kg)
Sleeping Kaolinite -1.9 Diamagnetic CuFeS ₂ 159 Quartz -0.58 Cu ₃ (AsO ₄ ) 4H ₂ O 995 Muscovite 1-15 CuHAsO ₃ 885 Montmorillonite 2.7 _{CuO · 2As 2 O 5 · 3H} 2 O 297 Vermiculite 15.2 Cr ₂ O ₃ · CaO 434 Cu ₂ (OH) ₂ CO ₃ 150 Paramagnetic Cr ₂ O ₃ · MgO 363 CuSO ₄ · 5H ₂ O 707 Fe (CN) ₆ K ₃ 125 CuO 377 Ilmenite (FeTiO ₃ ) 1,700 Antiferromagnetic Cu (OH) ₂ 150 Hematite (αFe ₂ O ₃ ) 6,300 Cr ₂ O ₃ 560 Goethite (αFeOOH) 8,600 NiSO ₄ 7H ₂ O 160 Lepidocrocite (γFeOOH) 7,500 Ni (OH) ₂ 610 Pyrrhotite (Fe ₇ S ₈ ) 39,000 Ferrimagnetic Cu ₅ FeS ₄ 105 Magnetite (Fe3O4) 100,000

Magnetic Properties of Soil Minerals and Heavy Metal Compounds

Minerals, which make up about 50% of the soil volume, are largely magnetic in nature, and diamagnetic minerals are difficult to be screened by magnetic fields. Paramagnetic, ferromagnetic, antiferromagnetic, and ferrimagnetic Minerals can be selectively extracted from the soil by controlling the intensity and gradient of the magnetic field.

Bityukova et al. (1999), Caggiano et al. (2005), Hanesh et al. (2002), Panaiotu et al. (2005), Xie et al. (2001) found a high correlation between soil mass ratio and heavy metals (Pb, Co, Cr, Ni, As, Cd, Cu, Zn).

The soil mass ratio is higher with higher mineral content in soil. The positive correlation between the large mass of soil and the content of heavy metals means that high mass minerals contain more heavy metals than low minerals. This phenomenon is explained by the presence patterns of soil heavy metals and the large autonomy of soil minerals. Heavy metals in soil have the most iron oxide and residual forms (ie, metal oxides, metal sulfates, and metal hydroxides), which have a relatively high susceptibility to silicate minerals.

The inventors have tested the relationship between the concentration of heavy metals (Ni, Zn, Pb, Cr) extracted from the soil by the aqua regia extraction method and the magnetic susceptibility of the soil, and the results are shown in FIGS. 13 to 16. The higher the concentration of heavy metal extracted from the soil, the higher the susceptibility of the soil. Referring to the graphs of FIGS. 13 to 16, it can be seen that the concentration of heavy metals and the mass ratio are in a proportional relationship.

From the above experimental results, it was confirmed that the soil particles in the dispersion can be separated into magnetic particles and non-magnetic particles through a magnetic separator.

After the magnetic separation step 40, the first solid-liquid separation step 50 and the second solid-liquid separation step 60 are performed. That is, in the first solid-liquid separation step 50, the suspension collected through the magnetic particle discharge pipe from the magnetic separator is put in a known centrifuge and the liquid (dispersion liquid) and the solid (soil particles) are separated using the difference in specific gravity. Similarly, in the second solid-liquid separation step 60, the suspension collected through the non-magnetic particle discharge pipe is put into a centrifuge and the solid-liquid separation is performed.

The soil particles separated in the second solid-liquid separation step 60 can be immediately recycled into the soil because it contains little heavy metal. However, it is safe to check whether these soil particles contain heavy metals above environmental standards, and if heavy metals above environmental standards are detected, separate treatment is required.

In addition, the liquid, that is, the dispersion liquid separated in the first solid-liquid separation step 50 and the second solid-liquid separation step 60 may be recycled again in the dispersion step 20. Since the dispersion should be guaranteed in a range of concentrations and pH as described above, it is possible to readjust the pH and concentration prior to recycling the dispersion to readjust the concentration and pH if out of the range.

After the first solid-liquid separation step 50, a heavy metal removal step 70 for extracting and removing heavy metals from magnetic soil particles is performed. In the heavy metal removal step 70, when the coarse soil particles separated in the particle size selection step 30 and the non-magnetic soil particles separated in the second solid-liquid separation step 60 are determined to contain heavy metals above environmental standards, Heavy metals can also be extracted from the soil. In the heavy metal removal step 70, it is possible to extract the heavy metal from the soil using a variety of known methods. As a method of extracting heavy metals, various methods may be adopted in a known manner, and thus detailed description thereof will be omitted.

As described above, when the heavy metal is extracted from the magnetic soil particles through the heavy metal removal step 70, the heavy metal contaminated soil restoration method according to the present invention is completed.

In the present invention, since only the magnetic soil particles are separated from the soil and the treatment is performed on the magnetic soil particles, there is an advantage that it is economical and effective as compared to the direct treatment of the entire soil to be treated.

In addition, the present invention has a great advantage that the magnetic separation can be effectively performed by going through the dispersion step prior to the magnetic separation.

In addition, secondary pollution, which is always a problem in the environmental pollution treatment technology, that is, the treatment problem for the chemicals used for treatment does not occur in the present invention has the advantage that it is very environmentally friendly. That is, the dispersion used in the present invention is recycled again, so that the problem of secondary processing does not occur.

Applicant has performed an experiment on the heavy metal removal efficacy of the contaminated soil restoration method according to the present invention.

That is, soils contaminated with arsenic in heavy metals were collected and dried in a room, and the sample was broken using a rubber stopper and a sample having a particle size of 2 mm or less using a standard mesh. To check the heavy metal concentration of the sample, the sample was extracted with heavy water using aqua regia, and the heavy metal concentration of the extract solution was measured using ICP-AES. The heavy metal concentration of the extract was converted to the heavy metal concentration of the soil, the value was confirmed as 322.9 mg / L as shown in the table of FIG.

Thereafter, 50 g of soil samples having a particle size of 2 mm or less and 200 mL of pH 11_10 mM sodium pyrophosphate solution were mixed and stirred for 5 minutes using a Soil mixer. After stirring, the granules were separated into fine and coarse matter by using a 63 μm standard mesh.

Some of the fine (<63 μm) and coarse (> 63 μm) soil samples were dried in an oven at 60 ° C. (solid-liquid separation was performed by oven drying), and heavy metals were extracted using aqua regia. The heavy metal concentration of the extract was measured using ICP-AES. The heavy metal concentration of the extract was converted to the concentration of the soil sample. As shown in FIG. 17, the heavy metal concentration of the soil particles having a size of 63 μm or more was 72 mg / L, and the heavy metal concentration of the soil particles of 63 μm or less was expected to be 403.3 mg / L. As the concentration of heavy metals was much higher.

Fine dry (<63 μm) soil sample suspensions were adjusted using a dispersion solution (pH 11 —10 mM sodium pyrophosphate) so that the concentration (weight) of the particles was 10%. A suspension with a 10% solids ratio was separated into magnetic and nonmagnetic materials at 12,000 gauss of magnetic field strength. After drying the magnetic suspension and the nonmagnetic suspension, heavy metals were extracted using aqua regia, and the concentrations of heavy metals in the extract were measured using ICP-AES. The heavy metal concentration of the extract was converted into the heavy metal concentration of the magnetic material and nonmagnetic material.

The concentration of heavy metals of magnetic particles less than 63μm was very high at 660.3mg / L, and the concentration of heavy metals of nonmagnetic particles less than 63μm was 256.1mg / L, much lower than that of magnetic particles. .

Although the present invention has been described with reference to one embodiment shown in the accompanying drawings, it is merely an example, and those skilled in the art may realize various modifications and equivalent other embodiments therefrom. I can understand. Accordingly, the true scope of protection of the present invention should be determined only by the appended claims.

100 ... How to restore heavy metal contaminated soil 10 ... Collection stage
20 ... dispersion step 30 ... granularity selection step
40 ... Magnetic separation step 50 ... First solid-liquid separation step
60 ... second solid-liquid separation step 70 ... heavy metal removal step

Claims (17)

A collection step of collecting soil contaminated with heavy metals;
A dispersion step of dispersing the soil inlets into a plurality of independent soil particles by releasing the cohesion between the plurality of soil particles by putting the collected soil in a dispersion; And
And a magnetic separation step of separating the soil particles by a magnetic field through a magnetic field of the suspension in which the soil particles and the dispersion liquid are mixed. The method of claim 1,
Between the dispersing step and the magnetic separation step, sifting the suspension into a network that can pass only the particles of a predetermined particle size or less, the particle sorting step of screening the soil particles, characterized in that it further comprises. The method of claim 2,
The mesh is a heavy metal contaminated soil restoration method characterized in that the size of the particles can pass through 50 ~ 125μm size. The method of claim 2,
The coarse soil particles filtered in the mesh is heavy metal contaminated soil restoration method characterized in that for recycling. The method of claim 1,
In the magnetic separation step,
By interposing the steel wool, which is bundled with wires between the electromagnets facing each other, the suspension passes through the steel wool while the electromagnet is powered on, thereby allowing magnetic soil particles in the suspension to adhere to the steel wool. ,
After the suspension has passed through the steel wool, the electromagnet is released and sprayed flushing liquid to the steel wool to collect the soil particles attached to the steel wool in the state contained in the flushing liquid. Heavy metal contaminated soil restoration method. The method of claim 5,
And solidifying the flushing liquid containing the magnetic soil particles after the magnetic separation step to solid-liquid separating the soil particles from the flushing liquid. The method of claim 5,
And a second solid-liquid separation step of collecting non-magnetic soil particles by solid-liquid separation of the suspension discharged from the magnetic separation step. The method of claim 7, wherein
The method of restoring heavy metal contaminated soil, characterized in that the suspension remaining after the soil particles are collected in the second solid-liquid separation step is recycled back to the dispersion of the dispersion step. The method of claim 8,
Heavy metal contaminated soil restoration method characterized in that the concentration is adjusted when the dispersion is recycled. The method of claim 7, wherein
The method for restoring heavy metal contaminated soil, characterized in that for recycling the non-magnetic soil particles collected in the second solid-liquid separation step. The method of claim 1,
The dispersion is a heavy metal contaminated soil recovery method characterized in that the alkaline solution. The method of claim 11,
PH of the dispersion is a heavy metal contaminated soil restoration method, characterized in that 8 to 12. The method according to any one of claims 1, 11 or 12,
The dispersion is a heavy metal contaminated soil recovery method characterized in that the phosphate solution. The method of claim 13,
The dispersion is pH 9 ~ 12 and the concentration is 5 ~ 50mM sodium hexametaphosphate (Na-hexametaphosphate) or sodium pyrophosphate (Na-pyrophosphate) characterized in that the soil restoration method for heavy metals. The method of claim 1,
The phosphate solution is a heavy metal contaminated soil restoration method characterized in that the anionic surfactant. 16. The method of claim 15,
The surfactant is pH 9 ~ 12, the concentration is 10 ~ 80mM heavy metal contaminated soil restoration method characterized in that. The method of claim 1,
And heavy metal removal step of extracting and removing heavy metals from the magnetic soil particles separated in the magnetic separation step.

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