JP2015128756A - Decontamination method of contaminated ground - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a decontamination method of contaminated ground which can apply an electric restoration method regardless of soil of the ground, and can remove and separate heavy metals.SOLUTION: A decontamination method of contaminated ground is a method to decontaminate polluted ground with hazardous materials, and includes: a step I using an agitating apparatus, churning and kneading the contaminated soil while injecting water if necessary, penetrating or drawing out to an appointed depth, and making uniform muddy ground; and a step II providing anodes and cathodes in an appointed gap in the muddy ground provided in the step I, and decontaminating it by electric restoration.

Description

  The present invention relates to a method for purifying contaminated ground contaminated with heavy metals.

  Ground contaminated by industrial wastewater may contain heavy metals such as cadmium, hexavalent chromium, lead, arsenic, boron, and cyanide. If such contaminated ground is left as it is, There is a risk that heavy metals contained in the water will diffuse into the environment through groundwater.

  Conventionally, there are known methods of excavating and removing ground contaminated with heavy metals, performing predetermined treatment outside the site, and disposing them, or insolubilizing or confining them in situ. The method of disposal outside the site has problems that vibration, noise, soil scattering, etc. occur during excavation, which has a large impact on the surrounding environment and is expensive. Also, in-situ insolubilization or containment methods do not eradicate contamination and still carry the risk of heavy metal contamination.

  In-situ flushing (soil flushing) is also known, in which washing water such as water and chemicals is circulated in the ground to collect heavy metals adsorbed on the soil gaps and soil particles. It cannot be applied to bad ground. The only in-situ purification technique for heavy metal-contaminated soils, regardless of the soil type such as sand layer, silt / clay layer, etc., is known as an electrical restoration method (Japanese Patent Laid-Open No. 2004-25149, etc.). The electrorepair method is positively and negatively ionized by three types of phenomena, electrolysis, electroosmosis and electrophoresis, which are generated by applying a DC voltage between the inserted anode and cathode after drilling into the contaminated ground. In this method, heavy metals and the like are moved to the anode and cathode, concentrated, separated and removed.

JP 2004-25149 A

  However, when the conventional electrical restoration method is applied to unsaturated ground, low moisture content ground or groundwater flow velocity, there is a problem that separation and removal of heavy metals are not sufficient. That is, conventionally, the electrical repair method does not function sufficiently.

  Accordingly, an object of the present invention is to provide a method for purifying contaminated ground, which can apply an electrical restoration method and can separate and remove heavy metals regardless of the soil quality.

  In such a situation, the present inventors have intensively studied, and as a result, the ground to which the electric restoration method is applied is stirred and kneaded using a stirrer while injecting water into the contaminated soil as necessary. The present inventors have found that the above-described conventional problems can be solved if the obtained uniform mud ground is used, and the present invention has been completed.

  That is, the present invention is a method for purifying ground contaminated with harmful substances, using a stirrer, stirring and kneading the contaminated soil, penetrating to or pulling out to a predetermined depth to form a uniform muddy ground. A method for purifying contaminated soil, comprising: I step to be performed; and II step of performing purification by electrical restoration by installing an anode and a cathode at predetermined intervals in the mud ground obtained in I step Is to provide.

  According to the present invention, an electric restoration method can be applied regardless of the soil quality of the ground, and heavy metals can be separated and removed.

It is a figure explaining I process of the purification method of contaminated soil in embodiment of this invention. It is a figure explaining II process of the purification method of the contaminated soil in embodiment of this invention. It is a boring simplified columnar figure of the target alternate layer ground in the reference example. The particle size accumulation curve of the code | symbol A part of FIG. 3 is shown. The particle size accumulation curve of the code | symbol B part of FIG. 3 is shown. The particle size accumulation curve of the code | symbol C part of FIG. 3 is shown. The particle size accumulation curve of the code | symbol D part of FIG. 3 is shown. It is a figure explaining the purification method of contaminated soil.

Next, a method for purifying contaminated soil in the embodiment of the present invention will be described with reference to FIGS. In the present invention, the ground Z ₁ to be purified may be any ground that is contaminated with harmful substances, and in particular, the ground that is contaminated with heavy metals such as cadmium, hexavalent chromium, lead, arsenic, boron, and cyan. The effect of the present invention is remarkably exhibited.

Examples of the contaminated ground Z ₁ include sand ground, silt / clay ground, and alternate layer ground. In the sand ground, sand particles are agglomerated, and even if the electric restoration method is applied as it is, separation and removal of heavy metals which are harmful substances are not sufficient. In addition, the silt / clay ground does not have a uniform gap, and even if the electrical restoration method is applied as it is, separation and removal of heavy metals that are harmful substances are not sufficient.

  Alternating ground is ground that includes a two-layer structure of sand, silt and clay, and in particular, that includes a three-layer structure of sand, silt, clay and sand. An embankment layer mainly composed of mixed sand may exist. The silt / clay layer is a silt layer or a clay layer or a layer in which silt and clay are mixed. If the electrical restoration method is applied to the alternate-layered ground as it is, the purification period depends on the electrode spacing, current density used, and soil quality. And the purification period becomes longer.

In the present invention, the step I uses the agitator 1 and agitates and kneads the water in the contaminated soil Z ₁ while injecting water as necessary, penetrates or pulls out to a predetermined depth, and forms a uniform mud ground Z _2. Is a step of forming. As the stirrer 1, a stirrer 1 equipped with a known stirrer blade 11, a known trencher, or a known water jet agitator used in a deep mixing treatment method or an underground columnar pile construction method can be used. As the stirring blade 11 in the stirring device 1 including the stirring blade 11, a two-stage blade of two blades (two) or a horizontal stirring blade of a three-stage blade is preferable. By using such a stirring device 1, it can be stirred mixing contaminated soil Z ₁ at a predetermined depth and predetermined diameter. Reference numeral 2 denotes a water supply device. Hereinafter, the purification method in the case of using the stirring apparatus 1 provided with the stirring blade 11 is demonstrated.

In Step I, to match the axis of the rotary shaft 12 of the stirring device 1 in the center of the agitation mixing point contaminated soil Z _1. Next, the rotating shaft 12 is penetrated into the ground while the stirring device 1 is driven to rotate the stirring blade 11. At this time, stirring and kneading while adding water as necessary. A mud ultra-soft ground can be formed by stirring and kneading while adding water as necessary. In addition, although the amount of water is determined in consideration of the moisture content contained in the soil and the stirring region, it is approximately 30% by volume at maximum with respect to the stirring and kneading ground.

  The stirring and kneading is at the time of penetration or at the time of withdrawal or at the time of penetration and at the time of withdrawal, preferably both at the time of penetration and at the time of withdrawal. The penetration speed and the drawing speed may be determined as suitable speeds for obtaining a highly uniform kneaded product. By such an operation, if it is sand ground, silt / clay ground, aggregated particles are solved, and a muddy ground having a uniform inter-particle gap is obtained. Moreover, if it is an alternating layer ground, gravel, fine-grained soil, and coarse-grained soil will fully be stirred, and the muddy ground in which the clearance gap between particle | grains exists uniformly will be obtained. The agitation and kneading zone of the alternate-layered ground eliminates the distinction between sand layers and silt / clay layers, resulting in ultra-soft soil.

  In step I, a water retention agent, a drug that dissolves heavy metals, or a drug that promotes ionization of heavy metals may be added simultaneously while stirring and kneading. As the water retention agent, known ones used in general civil engineering can be used. Moreover, the chemical | medical agent which dissolves a heavy metal, and the chemical | medical agent which accelerates | stimulates ionization of heavy metal can use the well-known thing used by the electrorepair method generally. The addition of the water retention agent can slow down the groundwater flow side in the formation where the groundwater flow velocity is fast, and can retain sufficient moisture in the formation where the water content ratio is low such as unsaturation. In addition, when inject | pouring a chemical | medical agent in I process, when a chemical | medical agent contains water, injection | pouring of single water can be skipped. In this case, water in the medicine becomes water to be injected. Further, in the step I, air stirring with an ejector can be made uniform due to the ejector lift effect.

In step I, a columnar underground kneaded body is obtained by stirring and kneading in the stirring device 1 (FIG. 1). The columnar underground kneaded body is a kneaded product of raw ground soil and water, and may contain gravel or the like contained in the embankment layer. The underground kneaded body naturally contains harmful substances. That is, columnar ground kneading body, many are formed in the contaminated ground Z _1, and preferably, formed in the contaminated area throughout. Thereby, the whole contaminated area can be made into a muddy ground, and heavy metal purification in the II step can be performed reliably. If a large number forming a columnar ground kneaded material in the contaminated ground Z _1, it is preferably formed of a wrap construction. That is, the underground kneaded body is preferably constructed in the entire contaminated area. Thus, contamination region to eliminate the non-construction part of the ground kneaded material, contaminated ground whole can be efficiently muddy ultra soft ground Z _2. The shape of the underground kneaded body of the present invention is, for example, a columnar pile, a rectangular wall body, a continuous construction body, and a lap construction body.

After I step, stirring and kneading the ground Z ₂ obtained is homogeneous slurry. Mud is a so-called fuzzy ultra-soft ground, and uniform means that the ground is initially kneaded by stirring and that there is substantially no large lump or large particle aggregate, This means that the gap is almost uniform. Homogeneous slurry ground _{Z 2} is the average water content of 20% or more, preferably 25% or more. The variation of the moisture content, that is, the difference between the maximum value and the minimum value of the moisture content is preferably 6% or less, and particularly preferably 3% or less. The amount of water added is adjusted according to the water content of the original ground. Muddy ground Z ₂ are inter-particle gaps are uniformly formed, also agglomerated particles are understood, in the electrical repair method step II, to facilitate electroosmosis and electrophoresis.

Step II is a step in which an anode and a cathode are installed at a predetermined interval in the mud ground obtained in Step I, and purification is performed by electrical restoration. Examples of the electrical repair method include known methods as described in JP-A-2004-25149. That is, as shown in FIG. 2, the electrolysis generated by applying a DC voltage 20 between the inserted pair of electrodes, the anode 21 and the negative electrode 22 after drilling, in the mud ground obtained in the step I. , Cation heavy metals Y ⁺ and Y ²⁺ such as zinc ion, copper ion and lead ion are moved to the cathode, and anion heavy metals X ⁻ such as cyan ion and chromium ion are moved to the anode by each phenomenon of electroosmosis and electrophoresis, It is concentrated and separated and removed. That is, the contaminated ground after Step I is a suspension of raw ground soil and water, and the interstitial water in the contaminated ground is uniformly distributed, and the electrolysis reaction is caused by the transfer of electrons to water molecules. Effectively occurs, heavy metals dissolve in pore water. In addition, heavy metals are adsorbed by electrostatic force on the surfaces of the individual soil particles that have been dissolved, and the cations and water can efficiently move to the cathode.
(Reference example)
The alternate ground (test ground) was selected by the boring survey and soil survey. FIG. 3 shows a simplified boring column diagram of the alternate layer ground. The ground shown in Fig. 3 has an embankment (sand mixed with gravel) layer, an embankment (sand mixed with gravel) layer, an embankment (silty sand) layer, a buried (fine sand) layer, Clay) layer and buried (sand) layer. Among these, the particle size accumulation curve of the embankment (silty sand) layer (symbol; A) is shown in FIG. 4, and the particle size accumulation curve of the buried soil (fine sand) layer (symbol; B) is shown in FIG. FIG. 6 shows the particle size accumulation curve of the upper part of the buried soil (clay) layer (symbol; C), and FIG. 7 shows the particle size accumulation curve of the lower part of the buried soil (clay sand) layer (symbol; D). . The groundwater level of this ground was -1.2m. In addition, the moisture content of the embankment (silty sand) layer (sign; A) is 14.8%, the moisture content of the upper part of the buried (clay) layer (sign; C) is 38.0%, and the depth is 6 The water content of the 0.0 m sand layer was 20.7%.

  Next, using a stirrer equipped with a three-stage stirring blade on both blades, the above-mentioned alternate layer ground is stirred and kneaded at the time of intrusion and withdrawing while adding 20% by volume of water, so that the ground is kneaded at 1.3 m in diameter. Formed body. The stirring device penetrated from the surface layer while stirring, and the substantial stirring and kneading zone was 5 m from a depth of 2 m to 7 m. The stirring and kneading time was 20 minutes. The rotational speed of the rotating shaft was 19 rpm when penetrating, 38 rpm when pulling, the penetrating speed was 0.4 m / min to 0.7 m / min, and the pulling speed was 0.6 to 1.1 m / min.

  Next, soil at points A, B, C, and D in the depth direction of the underground kneaded body was collected and subjected to particle size analysis. Moreover, the soil of the sand layer of depth 6.0m was extract | collected, and the moisture content was measured. The particle size accumulation curve of the corresponding portion of the embankment (silty sand) layer (symbol; A) in the underground kneaded body is shown in FIG. 4, and the corresponding portion of the buried (fine sand) layer (symbol; B) in the underground kneaded body 5 shows the particle size accumulation curve, and FIG. 6 shows the particle size accumulation curve of the upper part (sign: C) of the buried (clay) layer in the underground kneaded body. The particle size accumulation curve at the lower part of the (sand) layer (symbol: D) is shown in FIG. In addition, although the particle size analysis before and behind stirring kneading | mixing of each layer shown by code | symbol AD was performed also in three different different places in the same alternating layer ground area, each showed the same particle size accumulation curve.

From the result of point B in FIG. 5, it can be seen that the fine sand layer was homogeneous fine sand but became non-homogeneous and coarse particles by stirring and kneading. Moreover, it can be seen from the results of points C and D in FIGS. 6 and 7 that the clay layer was made of a homogeneous high-plastic clay and contained coarse particles by stirring and kneading. Moreover, although the upper part of the stirring kneaded material was heterogeneous and contained more coarse particles than the lower part, the soil particle gap was generally formed uniformly. In addition, the moisture content of the embankment (silty sand) layer (sign; A) is 25.6%, the moisture content of the upper part of the buried (clay) layer (sign; C) is 25.2%, and the depth is 6 The water content of the 0.0 m sand layer was 26.2%. The difference (variation) between the maximum value and the minimum value of the moisture content in this alternating layer ground was 1.0%. In addition, when a water retention agent is added during the stirring and kneading in the step I, the water content of the embankment (silty sand) layer (sign; A) is 29.0%, and the upper part of the buried (clay) layer (sign; The water content of C) was 30.6%, and the water content of the sand layer at a depth of 6.0 m was 25.4%. The difference (variation) between the maximum value and the minimum value of the moisture content in this alternate layer ground was 5.2%. Thus, the alternate layer ground caused dramatic composition change by the hydro-kneading.
(Underground kneaded body with lapping)
As shown in FIG. 8, seven underground kneaded bodies having a height of 5 m having a diameter of 1.3 m and a depth of 2 to 7 m were lapped on a virtual contaminated ground area Y having a diameter of about 3.5 m. The underground kneaded body subjected to wrapping is obtained by lapping six columnar underground kneaded bodies arranged in the circumferential direction with respect to one central columnar underground kneaded body.

  From the above reference example, the alternating layer ground after stirring and kneading had almost no large lumps or large soil particle aggregates, and the soil particle gaps were uniformly formed. For this reason, in the electric repair method, it is clear that ionization is promoted and heavy metals are easy to move.

  According to the present invention, an electric restoration method can be applied regardless of the soil quality of the ground, and heavy metals can be separated and removed. For this reason, the use of the site after purification is also expanded.

DESCRIPTION OF SYMBOLS 1 Stirring apparatus 2 Water supply apparatus 3 Alternating ground 10 Underground kneading body 33, 35 Sand layer 34 Silt and clay layer

Claims (8)

  A method of purifying the ground contaminated with harmful substances, using an agitator, agitating and kneading the contaminated soil, penetrating or withdrawing to a predetermined depth to form a uniform muddy ground, A method for purifying contaminated soil, comprising: a step II in which an anode and a cathode are installed at predetermined intervals in the muddy ground obtained in the step, and purification is performed by electrical restoration.   The method for purifying contaminated soil according to claim 1, wherein the stirring and kneading in the step I is performed while water is poured into the contaminated soil.   The method for purifying contaminated soil according to claim 1 or 2, wherein the muddy ground obtained in step I has a water content of 20% or more.   The method for purifying contaminated ground according to any one of claims 1 to 3, wherein a water retention agent is further added in the step I.   The method for purifying contaminated ground according to any one of claims 1 to 4, wherein in the step I, air agitation is further performed by an ejector.   The method for purifying contaminated ground according to any one of claims 1 to 5, wherein the step I performs lapping on the contaminated ground.   The method for purifying contaminated ground according to any one of claims 1 to 6, wherein in the step I, the muddy ground is formed over the entire contaminated ground.   The method for purifying contaminated ground according to any one of claims 1 to 7, wherein the contaminated ground is an alternating layer ground of a sand layer and a silt / clay layer.

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