JP2014079713A - Method for purifying contaminated soil and purifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove heavy metals from contaminated soil.SOLUTION: Arsenic is removed from contaminated soil 20 by dispersing soil grains 50 and colloids 52 which adsorb arsenic thereon, in ground water 18, and collecting the ground water 18 (contaminated water 19). In addition, a vibratory device 130 applies vibration to the ground water 18, thereby the dispersion of the soil grains 50 and the colloids 52 in the contaminated soil 20, which adsorb arsenic thereon, is accelerated, and as a result, arsenic 60 is effectively removed from the contaminated soil 20.

Description

  The present invention relates to a contaminated soil purification method and purification device.

  Patent Document 1 provides a water injection well for injecting water in the vicinity of a contaminated area that is contaminated with pollutants and below the groundwater level, and a pumping well is provided so that injected water from the water injection well passes through the contaminated area. An in-situ purification device for contaminated soil that purifies groundwater pumped from water by a water treatment system is described. And in this prior art, the technique which mixes a weak acidic substance or a weak alkaline substance in injection water, and promotes the elution to injection water of heavy metals etc. is disclosed.

  Patent Document 2 describes an in-situ purification method in which heavy metal-containing paddy soil is washed with a chemical aqueous solution and then washed with water. And in this prior art, the technique which adds and wash | cleans a chemical | medical-agent aqueous solution or water is disclosed so that the depth from a cultivation board to a water surface may be 35 cm or more.

  However, the above prior art has room for improvement in that the heavy metals are efficiently removed from the contaminated soil to purify the contaminated soil.

JP 2004-330084 A JP 2007-301491 A

  An object of the present invention is to efficiently remove heavy metals from contaminated soil in view of the above facts.

  The invention of claim 1 includes a water injection step of injecting water containing soil particles adsorbed with heavy metals and a dispersant for dispersing colloids into the contaminated soil, and the soil particles injected into the contaminated soil and adsorbed with the heavy metals And a recovery step of recovering the water in which the colloid is dispersed.

  In the first aspect of the present invention, water containing a dispersing agent that disperses the soil particles and colloids on which heavy metals are adsorbed is poured into the contaminated soil. By the dispersant contained in the water poured into the contaminated soil, the soil particles and colloids adsorbed with heavy metals are separated from the contaminated soil and dispersed in water. And the heavy metal is removed from contaminated soil by collect | recovering the water in which the soil particle and the colloid which adsorb | sucked the heavy metal were disperse | distributed.

  The invention according to claim 2 is characterized in that the dispersant is at least one of acrylic acid polymer, polycarboxylate, sodium humate, sodium lignin sulfonate, sodium hexametaphosphate, sodium pyrophosphate, and sodium tripolyphosphate. including.

  In the invention according to claim 2, heavy metals are adsorbed by acrylic acid polymer, polycarboxylate, sodium humate, sodium lignin sulfonate, sodium hexametaphosphate, sodium pyrophosphate, and sodium tripolyphosphate. Since the separated soil particles or colloids are separated and recovered in the liquid, the change in the pH of the soil is suppressed and separated as compared with the case where the heavy metals are eluted and recovered using acid or alkali. The environmental load is further suppressed in that it is easy to recover heavy metals. The acrylic acid polymer is neutral to weakly alkaline, and the acrylic acid polymer is desirable from the viewpoint of reducing the change in soil pH.

  According to a third aspect of the present invention, the heavy metal includes at least one of arsenic, selenium, fluorine, hexavalent chromium, boron, lead, mercury, cyan, and cadmium.

  In the invention described in claim 3, contaminated soil containing at least one of arsenic, selenium, fluorine, hexavalent chromium, boron, lead, mercury, cyan, and cadmium can be effectively purified.

  The invention according to claim 4 includes a vibration step for applying vibration to the water poured into the contaminated soil.

  In the invention described in claim 4, by imparting vibration to the water, the dispersion of the soil particles and colloid in which heavy metals are adsorbed from the contaminated soil is promoted.

  The invention according to claim 5 is a water injection well for injecting water containing soil particles adsorbed with heavy metals and a dispersant for dispersing colloids into the contaminated soil, and the soil particles injected into the contaminated soil and adsorbed with the heavy metals. And a pumping well for pumping up the water in which the colloid is dispersed.

  In invention of Claim 5, the water containing the dispersing agent which disperse | distributes the soil particle and colloid which heavy metal adsorb | sucked is poured into a contaminated soil with a water injection well. By the dispersant contained in the water poured into the contaminated soil, the soil particles and colloids adsorbed with heavy metals are separated from the contaminated soil and dispersed in water. And the heavy metal is removed from the contaminated soil by pumping and collecting the water in which the soil particles and the colloid dispersed in the heavy metal are absorbed in the pumping well.

  The invention of claim 6 is characterized in that the dispersant is at least one of acrylic acid polymer, polycarboxylate, sodium humate, sodium lignin sulfonate, sodium hexametaphosphate, sodium pyrophosphate, and sodium tripolyphosphate. Is included.

  In the invention of claim 6, heavy metals are adsorbed by acrylic acid polymer, polycarboxylate, sodium humate, sodium lignin sulfonate, sodium hexametaphosphate, sodium pyrophosphate, and sodium tripolyphosphate. Since the separated soil particles or colloids are separated and recovered in the liquid, the change in the pH of the soil is suppressed and separated as compared with the case where the heavy metals are eluted and recovered using acid or alkali. The environmental load is further suppressed in that it is easy to recover heavy metals. The acrylic acid polymer is neutral to weakly alkaline, and the acrylic acid polymer is desirable from the viewpoint of reducing the change in soil pH.

  According to a seventh aspect of the present invention, the heavy metal includes at least one of arsenic, selenium, fluorine, hexavalent chromium, boron, lead, mercury, cyan, and cadmium.

  In the invention of claim 7, contaminated soil containing at least one of arsenic, selenium, fluorine, hexavalent chromium, boron, lead, mercury, cyan, and cadmium can be effectively purified.

  The invention of claim 8 is provided with a vibration means for giving vibration to the water poured into the contaminated soil.

  In the eighth aspect of the invention, the dispersion of the soil particles and the colloid in which heavy metals are adsorbed from the contaminated soil is promoted by applying vibration to the water by the vibration means.

  According to the present invention, heavy metals can be efficiently removed from contaminated soil.

It is a schematic diagram which shows the purification apparatus concerning embodiment of this invention. It is a conceptual diagram which shows the state in which arsenic has adhered to the soil particle and the colloid. It is the table | surface which described the specification of the dispersing agent. It is a graph which shows the arsenic density | concentration of the polluted water (groundwater) pumped up from a pumping well, and the arsenic collection | recovery cumulative amount. It is explanatory drawing which shows the experiment which confirms that arsenic has adhered to the soil particle and the colloid in order to (A)-(E). It is explanatory drawing explaining the experiment which confirms the removal effect of the arsenic by a dispersing agent. It is a graph which shows the result of the experiment shown in FIG.

  A contaminated soil purification method and purification apparatus according to an embodiment of the present invention will be described.

[soil]
As shown in FIG. 1, the upper side of the water level S of the ground water 18 in the ground 10 is a water permeable layer 12 made of sand, silt or the like. Further, below the groundwater level S in the ground 10 is an aquifer 14 composed of soil particles 50, colloids 52 (see FIG. 2) and gravel. In addition, the water permeability of the aquifer 14 of this embodiment is 10 ⁻⁴ cm / second or more.

  In the aquifer 14, there is contaminated soil 20 containing arsenic 60 (see FIG. 2), which is a heavy metal. The contaminated soil 20 is formed at a depth of about 3 m to 5 m from the ground surface. Further, under the contaminated soil 20 is non-contaminated soil 15 having relatively low water permeability. Non-contaminated soil is soil that conforms to the soil environmental standards for contaminants (arsenic 60 in this embodiment).

  As shown in FIG. 2, in the contaminated soil 20, arsenic 60 contained in the contaminated soil 20 is adsorbed on the fine soil particles 50 and the colloid 52. Arsenic 60 has a negative charge by ionization, and fine soil particles 50 and colloid 52 have a positive charge by ionization of iron contained therein. The arsenic 60 having a negative charge is electrically adsorbed on the soil particles 50 and the colloid 52 having a positive charge.

[Purification device]
As shown in FIG. 1, the purification device 100 according to the present embodiment includes a water injection well 110, a pumping well 120 that pumps groundwater 18 from the contaminated soil 20, and a vibration device 130 that vibrates the groundwater 18 of the contaminated soil 20. ing. In FIG. 1, pumping wells 120 are provided at intervals on both sides of the water injection well 110. However, the arrangement of FIG. 1 is an example, and is not limited to this configuration.

  The water injection well 110 injects into the contaminated soil 20 water 80 containing a dispersant that disperses the fine soil particles 50 and the colloid 52 (see FIG. 2) in the ground water 18 (hereinafter may be referred to as “washing water 80”). .

  The dispersant of the present embodiment uses a neutral to weakly alkaline acrylamide-based acrylic acid polymer. Specifically, “Telflow E” manufactured by Ternite Co., Ltd. is used. The details of Telflow E are shown in FIG.

  As shown in FIG. 1, the water injection well 110 and the pumping well 120 are provided such that the lower end portions 110 </ b> A and 120 </ b> A reach the uncontaminated soil 15 below the contaminated soil 20. Further, the pumping well 120 is provided so that the cleaning water 80 injected from the water injection well 110 passes through the contaminated soil 20.

  Knitted screens 112 and 122 are provided at positions corresponding to the depth of the contaminated soil 20 in the water injection well 110 and the pumping well 120, respectively. Then, the washing water 80 is discharged from the screen 112 of the water injection well 110 to the contaminated soil 20 and the ground water 18 is sucked from the screen 120 of the pumping well 120. In addition, by providing the screens 112 and 122, entry of soil into the water injection well 110 and the pumping well 120 is prevented.

  The vibration device 130 includes a steel pipe 132 and a vibration source 134. The pipe 132 is provided between the water injection well 110 and the pumping well 120, and is embedded so that the lower end portion 132 </ b> A reaches the non-contaminated soil 15 below the contaminated soil 20.

  The pipe 132 as a whole vibrates by vibrating the upper end 132B protruding to the ground by the vibration source 134. And the vibration of this pipe 32 is transmitted to the ground water 18 of the contaminated soil 20, and the ground water 18 vibrates.

  Note that the vibration device 130 is not limited to such a configuration. Any device may be used as long as the groundwater 18 of the contaminated soil 20 can be vibrated and the groundwater 18 can vibrate.

[Purification method]
Wash water 80 is poured from the water injection well 110 into the contaminated soil 20 by a pump (not shown). By the dispersing agent (see FIG. 3) contained in the washing water 80 poured into the contaminated soil 20, the soil particles 50 and the colloid 52 (see FIG. 2) in which the arsenic 60 is adsorbed in the contaminated soil 20 are separated, and the groundwater 18 To disperse.

  From another viewpoint, instead of separating the arsenic 60 from the soil particles 50 and the colloid 52 and extracting the arsenic 60 into the groundwater 18, the soil particles 50 and the colloid 52 adsorbed by the arsenic 60 are dispersed in the groundwater 18 to form the groundwater 18. Arsenic 60 is extracted.

  At this time, the ground water 18 is vibrated by vibrating the pipe 132 of the vibration device 130, thereby promoting the dispersion of the soil particles 50 and the colloid 52 into the ground water 18.

  Then, the ground water 18 (contaminated water 19) in which the arsenic 60 (see FIG. 2) is adsorbed and the colloid 52 is dispersed is pumped from the pumping well 120 by a pump (not shown) and collected. Arsenic 60 (see FIG. 2) is removed.

  The soil particles 50 adsorbed by the arsenic 60 collected by the pumping well 120 and the contaminated water 19 in which the colloids 52 are dispersed are treated in a coagulation sedimentation treatment facility or the like provided in another place. In addition, the process which removes the arsenic 60 from the contaminated water 19 may be performed locally, and water may be poured into the ground 10 and returned.

<Action and effect>
Next, the operation and effect of this embodiment will be described.

  The soil particles 50 and the colloid 52 (see FIG. 2) to which the arsenic 60 has been adsorbed are dispersed in the ground water 18 and the ground water 18 (contaminated water 19) is recovered, so that the arsenic 60 is separated from the soil particles 50 and the colloid 52, for example. Compared with the case where the groundwater 18 is extracted, the arsenic 60 is effectively removed from the contaminated soil 20.

  Further, by applying vibration to the groundwater 18 by the vibration device 130, the dispersion of the soil particles 50 and the colloid 52 adsorbed by the arsenic 60 of the contaminated soil 20 into the groundwater 18 is promoted. As a result, the arsenic 60 is absorbed from the contaminated soil 20. Further effectively removed.

  Moreover, the change of pH of the ground 10 can be made small by using an acrylic acid-type polymer as a dispersing agent (refer FIG. 3).

  From another viewpoint, since the soil particles 50 and the colloid 52 adsorbed by the arsenic 60 are separated and recovered by dispersing them with a dispersant, the arsenic 60 is eluted and recovered using acid or alkali. Thus, the environmental load is further suppressed in that the change in pH of the ground 10 is suppressed and the separated arsenic 60 can be easily recovered.

[Contamination result of contaminated soil]
Next, a result of confirming that arsenic 60 has been removed and purified from the contaminated soil 20 of the ground 10 will be described.

  FIG. 4 is a graph showing the concentration of arsenic 60 (see FIG. 2) in the contaminated water 19 (see FIG. 1) pumped in the pumping well 120 and the total amount of arsenic 60 recovered. In addition, the graph of (A) is the result of the contaminated water 19 pumped up by one pumping well 120, and (B) is the result of the contaminated water 19 pumped up by the other pumping well 120. In addition, the horizontal axis indicates the passage of time (weeks).

  From the graph shown in FIG. 4, the concentration of arsenic in the contaminated water 19 (ground water 18) becomes almost 0 (zero) in about the 9th week, and the accumulated recovery amount is saturated. That is, it can be seen that the removal of arsenic 60 from the contaminated soil 20 that can be removed by the present invention has been completed (the soil after the purification was collected and analyzed, and the soil environmental standards were satisfied. You know it ’s done).

[Verification experiment of arsenic adsorption on soil particles and colloids]
Next, the results of an experiment confirming that arsenic 60 contained in the contaminated soil 20 is adsorbed on the fine soil particles 50 and the colloid 52 will be described.

The experiment was conducted in accordance with 2003 Ministry of the Environment Notification No. 18 to prepare and measure filtrate (test solution based on Ring No. 18). Specifically, the following procedure was used.
As shown in FIG. 5 (A), the contaminated soil 20 is collected and air-dried, and passed through a non-metallic 2 mm sieve 150.
As shown in FIG. 5B, the sieved soil 20A and the solvent 152 are mixed at a ratio by weight of 10%. The solvent 152 is obtained by adding hydrochloric acid to pure water so that the hydrogen ion concentration index is 5.8 or more and 6.3 or less.
As shown in FIG. 5C, the mixture 22 of the soil 20A and the solvent 152 is continuously shaken for 6 hours under conditions of 200 times per minute with a swing width of 4 to 5 cm at normal temperature and normal pressure.
As shown in FIG. 5D, the mixture 22 is further centrifuged at 3000 rpm for 20 minutes.
As shown in FIG. 5E, the supernatant of the centrifuged mixture 22 is filtered through a membrane filter 154 having a pore size of 0.45 μm.

  This filtered filtrate 24 is a test solution based on Ring No. 18. The filtrate 24 (test solution) is cloudy because there are fine particles that have passed through the 0.45 μm membrane filter 154, that is, fine soil particles 50 and colloids 52 (see FIG. 2). As a result of quantitative analysis of the filtered liquid 24, the arsenic concentration was 0.019 mg / L. Further, the filtered liquid 24 was further centrifuged for 2 hours, and the arsenic concentration of the transparent supernatant was 0.006 mg / L.

  Thus, it was confirmed that the arsenic 60 was adhered to the fine particles of 0.45 μm or less that passed through the filter from the contaminated soil 20, that is, the fine soil particles 50 and the colloid 52.

[Effect of dispersant]
A verification experiment of the removal effect of arsenic 60 by the dispersing action of the washing water 80, that is, the dispersing agent (acrylic acid polymer (“Terflow E” manufactured by Ternite Co., Ltd.)) will be described.

  As shown in FIG. 6, the experimental apparatus 160 includes a column 162, a pump 170, and a liquid container 172. The column 162 is filled with contaminated soil 20. Further, glass wool 166 is provided at the drain side end of the column 162. Washing water (water containing a dispersing agent) 80 is placed in the liquid container 172. Then, the pump 170 measures the amount of arsenic 60 (see FIG. 2) in the drained water that has been passed through the glass wool 166 and passed through the glass wool 166. The fine soil particles 50 and the colloid 52 pass through the glass wool 166. As a comparative example, the same experiment was performed using water containing no dispersant.

  The experimental results are shown in the graph shown in FIG. The horizontal axis of the graph indicates the number of water passes (water flow rate / soil gap), and the vertical axis indicates the cumulative amount (mg) of arsenic in the drainage. As can be seen from this graph, the arsenic 60 was removed about seven times more in the cleaning water 80 than in the water. The target arsenic removal amount of 2.1 mg was cleared by passing water 10 times. The target arsenic removal amount is an amount necessary to achieve the soil environmental standard (0.01 mg / L or less).

  As described above, it was confirmed that the soil particles 50 and the colloid 52 adsorbed with the arsenic 60 are dispersed in the washing water 80 and discharged. Further, it was confirmed that the effect of discharging arsenic 60 was low even when water containing no dispersant was passed. That is, the removal effect of the arsenic 60 by the dispersing action of the washing water 80, that is, the dispersant (acrylic acid polymer (“Terflow E” manufactured by Ternite Co., Ltd.)) was confirmed.

  In addition, from this experiment, the soil environment standard (0.01 mg / L or less) in the local ground 10 is determined from the amount of water passing the target arsenic removal amount of 2.1 mg and the amount of contaminated soil 20 filled in the column 162. It is possible to calculate the amount of water necessary for clearing.

<Others>
The present invention is not limited to the above embodiment.

In the said embodiment, although the acrylic polymer (refer FIG. 3) was used for the dispersing agent, it is not limited to this. However, acrylic acid-based polymers are neutral to weakly alkaline, and acrylic acid-based polymers are desirable from the viewpoint of reducing changes in soil pH.
The dispersant is not particularly limited as long as it is useful for dispersion of soil particles and colloids, but polycarboxylic acid and its salt, humate, lignin sulfonate, hexametaphosphate, pyrophosphate, and Examples thereof include compounds selected from tripolyphosphates, and preferred salts include alkali metal salts such as sodium salts and potassium salts, and carbonates.
More specifically, an aqueous phosphate solution such as a sodium hexametaphosphate solution, a sodium pyrophosphate solution, or a sodium tripolyphosphate solution may be mentioned. The polycarboxylic acid is preferably a polymer comprising a monomer derived from acrylic acid, a polyacrylic acid which is a copolymer, its sodium salt, potassium salt, or the like.
In particular, when polyacrylic acid and its salts, which are polycarboxylate-based polymer compounds, are dispersed and dissolved in water, they exhibit neutral to weakly alkaline properties, and changes in soil pH may cause other dispersants. Compared to the above, it is preferable because it can be kept low, and the adsorbability and dispersion stability with respect to the soil particles are good.
The dispersant that can be used in the present invention is also available as a commercial product. For example, as a polycarboxylic acid compound, telflow E (trade name: manufactured by Ternite Co., Ltd .: polycarboxylic acid / polyester) is known as a cement dispersant. Acrylate complex), Terflow MX (trade name: manufactured by Ternite: polycarboxylic acid carbonate), Aron AK flow / AK flow (B) (trade name: manufactured by AK Techno, polycarboxylate / sodium bicarbonate / carbonate Soda), Leoflow A-1000 (trade name: manufactured by Lion, polycarboxylic acid polymer aqueous solution), Geosper F1, K (trade name: manufactured by Floric, polycarboxylic acid polymer compound, oxycarboxylate) Etc., and these can be suitably used in the present invention.
Further, washing water containing a plurality of types of dispersants may be poured.

  In the above embodiment, the heavy metal contained in the contaminated soil 20 is arsenic 60, and the present invention is applied to the removal of the arsenic 60, but the present invention is not limited to this. For example, the present invention can be applied to the removal of selenium, fluorine, hexavalent chromium, boron, lead, mercury, cyanide, and cadmium. The present invention can also be applied to purification of contaminated soil containing a plurality of types of heavy metals. In other words, the present invention can be applied to purification of heavy metals attached to soil particles and colloids.

  In the above embodiment, the ground water 18 is vibrated by the vibration device 130 to promote the dispersion of the soil particles 50 and the colloid 52 adsorbed by the arsenic 60 into the ground water 18, but is not limited thereto. The vibration device 130 may not be provided (installation of the vibration device 130 is not essential).

  Furthermore, it cannot be overemphasized that it can implement with a various aspect in the range which does not deviate from the summary of this invention.

10 Ground 20 Contaminated soil 50 Soil particles 52 Colloid 60 Arsenic (an example of heavy metals)
80 Washing water (water containing dispersant)
DESCRIPTION OF SYMBOLS 100 Purification apparatus 110 Water injection well 120 Pumping well 130 Vibration apparatus (an example of vibration means)

Claims (8)

A water injection process for injecting water containing a dispersing agent for dispersing soil particles and colloids adsorbed with heavy metals into the contaminated soil;
A recovery step for recovering the water in which the soil particles and the colloids dispersed therein are poured into the contaminated soil and adsorbed by the heavy metals;
A method for purifying contaminated soil. The dispersant includes at least one of acrylic acid polymer, polycarboxylate, sodium humate, sodium lignin sulfonate, sodium hexametaphosphate, sodium pyrophosphate, and sodium tripolyphosphate.
The method for purifying contaminated soil according to claim 1. The heavy metals include at least one of arsenic, selenium, fluorine, hexavalent chromium, boron, lead, mercury, cyan, and cadmium.
The purification method of the contaminated soil of Claim 1 or Claim 2. Comprising a vibration step of vibrating the water poured into the contaminated soil,
The method for purifying contaminated soil according to any one of claims 1 to 3. A water injection well for injecting water containing a dispersing agent for dispersing soil particles and colloids adsorbed with heavy metals into the contaminated soil;
A pumping well for pumping up the water in which the soil particles and the colloid dispersed are poured into the contaminated soil and adsorbed by the heavy metals;
A purification device comprising: The dispersant includes at least one of acrylic acid-based polymer, polycarboxylate, sodium humate, sodium lignin sulfonate, sodium hexametaphosphate, sodium pyrophosphate, and sodium tripolyphosphate.
The purification device according to claim 5. The heavy metals include at least one of arsenic, selenium, fluorine, hexavalent chromium, boron, lead, mercury, cyan, and cadmium.
The purification apparatus according to claim 5 or 6. Comprising vibration means for vibrating the water poured into the contaminated soil,
The purification apparatus of any one of Claims 5-7.

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