JP6434255B2 - Extraction method of harmful heavy metals in soil - Google Patents

Description

  The present invention relates to a method for extracting harmful heavy metals from soil as an on-site soil cleaning method.

  One of the on-site methods for cleaning soil containing toxic heavy metals is a soil cleaning method, in which contaminated soil is mechanically cleaned and sieved, and toxic heavy metals are mainly adsorbed and concentrated. There are classified cleaning methods that separate and remove particles, and chemical extraction methods that extract and remove harmful heavy metals by rinsing with a cleaning solution that contains chemicals and can elute harmful heavy metals.

  The following patent document shows an example of a chemical extraction method, and a predetermined area is defined to have an appropriate size so that it can correspond to the amount of contaminated soil to be purified and the treatment capacity of the purification treatment facility F. A partition wall is set up for this purpose.

  Next, cleaning liquid injection holes set to a desired number and a desired depth so as to conform to the horizontal and vertical concentration distributions of the contaminants are excavated, and the cleaning liquid tank is disposed near the opening on the ground of the cleaning liquid injection holes 6. Inject the cleaning solution.

After injecting the cleaning solution, leave it for a certain period of time necessary for the cleaning solution to elute the contaminants from the contaminated soil 9, observe the change over time, and transfer it to the purification facility before the predetermined amount. The treated soil is excavated and the same operation is sequentially repeated for each defined section.
JP 2004-57953 A

  In this patent document 1, as shown in FIG. 7, as for the soil washing system in the purification treatment facility F which processes the pretreated soil 12, all the treated pretreated soil 12 elutes a pollutant. It is carried into a state purification treatment facility F that is easy to clean and is cleaned to the extent that it satisfies the environmental standards.

  First, the pretreated soil 12 excavated from the defined section of the contaminated area B in Step 15 or Step 18 is transported to the purification treatment facility F by a transport vehicle such as a dump truck (Step 19).

  Regarding the process in the purification treatment facility F, first, the mixture of the pretreated soil 12 and the cleaning liquid 11 is put into a classifier 16 such as a vibration sieve to classify coarse and fine particles (step 20). Then, the coarse particles and a part of the fine particles are further washed with a washing solution in, for example, the drum type washing device 17 (step 21), and the remainder of the fine particles is finally disposed of outside the field (step 22). The

  Part of the coarse particles and fine particles whose concentration has been reduced to a level that satisfies the environmental standards through step 21 has increased the solubility of the contaminants in the purification process. Since it cannot be used for reuse such as returning, insolubilization processing is finally performed in the drum type cleaning device 18 (step 23).

  Here, the discharged cleaning solution from the drum type cleaning device 17 and the discharged insolubilized solution from the drum type cleaning device 18 are collected and temporarily stored in the reservoir 19, and then each cleaning solution processing facility 20, insolubilized solution processing. It is processed (step 24) in the facility 21 and reused.

  In addition, the waste liquid after reuse is subjected to a process (step 25) for separating contaminants in the water treatment facility 22 together with the cleaning liquid used in the pre-treatment in-situ collected from the classifier 16. In addition, the sludge containing the pollutant is properly disposed of by a predetermined method (step 26), and the treated waste water is discharged into the sewer or the like (step 27).

  On the other hand, the coarse particles and a part of the fine particles insolubilized in the drum type cleaning device 18 are collected as the final treated soil 13 and transported to the original contaminated area to be reused (for example, refilled). Step 28) is performed.

In addition, the following patent document is proposed as an advantage that the processing efficiency is remarkably high and the construction cost is remarkably low as compared with the conventional example because it is a very simple method of simply putting mud etc. into the water-permeable bag. The contaminated mud or contaminated mud water containing harmful substances showing the property of adhering to the particles is put into the permeable bag by using a pump, etc. In addition to passing through the bag body and dewatering, particles in the mud or mud water and harmful substances attached thereto remain in the bag body so that the harmful substances can be contained in the bag body 5.
JP 2002-178000 A

  In Patent Document 2, mud is taken out by a dredger, supplied to a processing pit provided in advance on the shore via a pressure feed hose, and temporarily stored. Subsequently, the toxic substance-containing mud deposited in the treatment pit is sucked and pumped by the injection pump and sequentially injected into the permeable bag through the injection pipe.

  Thereby, only moisture is permeated and discharged out of the bag body, and harmful substances are attached to the soil particles and the like, so they remain in the bag body together with these particles and are contained in the bag body.

In addition, as an example in which large soil bags are used as a container for the purpose of solid-liquid separation, there is a bagging dewatering method for promoting dewatering of mud in the following patent document.
JP 2002-178000 A

  Patent Document 3 relates to a method for dehydrating clay in a bag, particularly a method for quickly dehydrating clay having a high water content ratio in a water-permeable bag and comprising a non-woven material that allows only moisture to permeate. After the sludge is put into a sludge treatment bag formed by forming a sheet into a bag shape, the mouth of the bag is tied, and when the sludge-filled bag is left to stand, the elongated shape along the bag between each bag Insert a water permeable layer.

  In the classification cleaning method, it is necessary to physically classify the contaminated soil for each particle size, so that the increase in processing costs associated with the installation of the machine by installing a large number of machine equipment such as screens, belt feeders, cyclone units, etc. Due to the large area occupied by the equipment, there are many cases where there are significant restrictions on the application in narrow land, and the on-site applicability is limited.

  Further, in the example of Patent Document 1 shown as a chemical extraction method, a mechanical configuration similar to the classification cleaning method is required in principle after the immersion treatment (chemical extraction with citric acid). In other words, a drum-type cleaning device (equivalent to the cyclone unit of the classification cleaning method) and a classification device for separating coarse and fine particles are necessary, and although it can be scaled down, it is still applicable on-site. It was something that left constraints.

  Moreover, in patent document 2, it is what press-fits into a water-permeable bag body using a pump etc., and a soil adsorbing environmental pollutant is confined in soil soil in the process of consolidation dehydration of the contaminated mud soil isolated to soil soil. However, this does not selectively transfer harmful substances out of the sandbag.

  Further, Patent Document 3 discloses that soil-absorbing environmental pollutants are confined in the soil in the process of compacting and dewatering the contaminated mud isolated in soil, but there is nothing about cleaning of toxic heavy metals. Not considered.

  However, Patent Document 3 discloses only the effect of compaction dehydration and sieving, and does not show the utility as a soil holding container during cleaning of harmful heavy metals.

  The object of the present invention is to eliminate the inconvenience of the conventional example, and to use a sandbag as a soil holding container during washing of toxic heavy metals, thereby limiting the on-site applicability in the classification process. An object of the present invention is to provide a method for extracting harmful heavy metals in soil that can simplify the classification process after washing by holding contaminated soil with a large sandbag that also serves as an immersion container in a washing tank.

In order to achieve the above object, the present invention according to claim 1 is capable of (1) putting contaminated soil containing harmful heavy metals in a sandbag formed of a water-permeable material, and (2) extracting harmful heavy metals from the contaminated soil. The soil containing the contaminated soil is immersed in the washing solution for a certain period of time and washed to chemically extract and remove toxic heavy metals from the contaminated soil. (3) (1) Put contaminated soil containing toxic heavy metals in the soilbag formed of water-permeable material, so that solid-liquid separation can be realized without special mechanical equipment by remaining in the soilbag without flowing out, (2) Dipping the soil soil containing the contaminated soil into a tank containing a cleaning solution capable of extracting hazardous heavy metals from the contaminated soil for a certain period of time, and inserting a permeation tube into the soil soil, Draw out wash water and let it flow back These harmful heavy metals was chemically extracted and removed from the contaminated soil, (3) by the original contaminated soil cleaned remain in the sandbags without flowing out sandbags, resulting in solid-liquid separation otherwise The gist is to realize without mechanical equipment.

  According to the first aspect of the present invention, by using a sandbag as a soil holding container during washing of toxic heavy metals, soil holding during washing and solid-liquid separation after washing can be performed only by sandbags having drainage performance. As a result, it is no longer necessary to use mechanical equipment that was necessary in the past, and the on-site applicability is expanded.

  Moreover, a water channel can be formed without using an additive by inserting a water-permeable tube into the soil, sucking out the washing water from the soil center and refluxing it.

  The gist of the present invention described in claim 2 is to remove the cleaning liquid remaining on the soil by rinsing with tap water or water charged with a surfactant after soaking for a certain period of time. .

  According to the second aspect of the present invention, the washing liquid remaining in the sandbag is removed by rinsing with tap water or water charged with a surfactant or the like. At this time, the soil soil in which the contaminated soil has drainage performance is removed. Therefore, when immersion and rinsing of the treated soil are completed, solid-liquid separation can be achieved even without mechanical equipment.

The gist of the present invention described in claim 3 is that the sandbag is a large sandbag having a capacity of about 1 m ³ .

  According to this invention of Claim 3, it can carry out efficiently by using a large sandbag.

  The gist of the present invention described in claim 4 is that the cleaning solution uses an acid extract such as hydrochloric acid, sulfuric acid, acetic acid or the like that can dissolve and extract the chelating agent or heavy metals.

  According to the fourth aspect of the present invention, it is known that the chelating agent forms a very stable chelate complex with heavy metal ions, and this high heavy metal extraction effect can be utilized. In place of the chelating agent, an acid extract such as hydrochloric acid, sulfuric acid or acetic acid capable of dissolving and extracting heavy metals can also be used.

  As described above, the method for extracting harmful heavy metals in soil according to the present invention uses the sandbag as a soil holding container during washing of harmful heavy metals, thereby limiting the on-site applicability in the classification process. The classification process after washing can be simplified by holding contaminated soil with a large sandbag that also serves as an immersion container in the washing tank without using such a mechanical device.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory view showing an embodiment of the method for extracting harmful heavy metals in soil according to the present invention. In the figure, 1 is a large soil bag made of a water permeable material and having a capacity of about 1 m ³ , and 2 is a cleaning liquid 4. Tank.

  First, the contaminated soil 3 containing harmful heavy metals is put in the sandbag 1.

A tank 2 containing a cleaning solution 4 capable of extracting harmful heavy metals from the contaminated soil is prepared. The size of the tank 2 may be a size that can accommodate a large sandbag with a capacity of about 1 m ³ .

  The soil container 1 containing the contaminated soil 3 is placed in the tank 2 and immersed in the cleaning solution 4 for a certain period of time for cleaning, and harmful heavy metals are chemically extracted and removed from the contaminated soil.

  The cleaning liquid 4 can extract harmful heavy metals from contaminated soil, and is an acid extraction liquid such as hydrochloric acid, sulfuric acid, and acetic acid that can dissolve and extract chelating agents or heavy metals.

  In this way, the hazardous heavy metals are chemically transferred from the contaminated soil 3 to the washing solution, extracted and removed, and then rinsed with the rinsing water 5 into which tap water or a surfactant is added, and remain in the sandbag. Remove the cleaning solution.

  At this time, since the contaminated soil is held in a sandbag having drainage performance, solid-liquid separation can be achieved without mechanical equipment as a result of completion of immersion and rinsing of the treated soil.

  In this invention, it becomes a subject that immersion washing | cleaning and a rinse can be implemented reliably in the state hold | maintained in the soilbag which has draining performance. Therefore, when targeting soils with low gaps (such as viscous soils) that are relatively difficult to wash and rinse, a polymer swelling agent (such as a superabsorbent polymer such as sodium polyacrylate) Coarse grains with a large porosity (lightweight concrete crushed material, etc.) are added to artificially form a water channel in the immersion of the cleaning liquid.

  In addition, when the contaminated soil is washed, the apparent volume decreases due to the compaction and homogenization of the soil, and an increase in the amount of soil from the soil may be required to refill the original position. In that case, the volume can be increased with these additives.

  FIG. 2 shows another embodiment of the present invention. As a method of forming a water channel without using an additive, a water permeable tube 6 is inserted into a sandbag 1 and the washing water is sucked out from the center of the soil by a pump 7. There is also a method of refluxing.

  Washing of the sandbag 1 in the tank 2 may be performed by simply stirring, or by stirring, and stirring may be performed manually or mechanically.

An experiment for confirming the effect of the present invention will be described below.
The extraction treatment method using a chelating agent was examined as an on-site treatment method for heavy metal-contaminated soils that can be applied with simple equipment, which can be applied at sites with narrow rainfall and a relatively small amount of treated soil.

  Chelating agents are known to form very stable chelate complexes with heavy metal ions, and are applied to soil remediation using this high extraction effect of heavy metals.

(Soil properties for the experiment)
Table 1 shows the properties of lead-contaminated soil (soil A and B) used in the laboratory experiments. Soil A and B were collected in the vicinity of the same site, and the soil that was passed through a 5 mm sieve in a solid state was used. As a representative sample, the particle size accumulation curve of soil A is shown in FIG.

  As the soil classification, sandy soil with a silt / clay fine particle content of less than about 10% was suitable for normal soil washing.

  Reagent preparation EDTA was used as a chelating agent used for lead extraction. Using EDTA · 4Na as a reagent, it was adjusted to a concentration of Pb: EDTA = 1: 10 (0.00844 mol / L) with respect to the lead content in soil A (value of Circular 19). The chelate washing solution when used for soil B was also prepared to a concentration (0.0049 mol / L) at a molar ratio of Pb: EDTA = 1: 10. In addition, tap water was used for all the water used for the laboratory experiment.

(experimental method)
The extraction conditions in the laboratory experiment were performed in a way that imaged the extraction operation when applied to actual construction. Specifically, three types of extraction method (1): dipping method, extraction method (2): manual stirring, and extraction method (3): mechanical stirring were set. Extraction method (1) puts contaminated soil in a sandbag, puts the sandbag into a tank containing EDTA extract and immerses it, Extraction method (2) puts soil in the EDTA extract in the tank This is an image of stirring with a backhoe. The extraction method (3) is an extraction image performed in order to grasp the maximum extraction effect when ideal stirring is performed. In addition, in extraction method (3), it implemented about the case where EDTA extract was used and the case where EDTA extract was not put (only tap water was used as control). Details of the extraction operation for each extraction method are described below.

1) Extraction method (dipping method)
Place a mesh bag (with an opening of about 1 mm) containing soil A (200 g) in a beaker containing 400 mL of EDTA extract so that the ratio of soil to extract is 1: 2, and soak for 24 hours. Two cases were carried out. After the immersion time, the soil was taken out together with the mesh bag. The soil in the removed mesh bag was put into a beaker containing 400 mL of water and rinsed (immersion for 30 minutes). FIG. 4 shows an operation flow.

2) Extraction method (hand stirring)
Two cases were carried out in which soil A (200 g) was placed in a beaker containing 400 mL of EDTA extract and stirred 5 times and 10 times with a spoonful so that the ratio of soil to extract was 1: 2. After stirring for 30 minutes, the soil was taken out from the EDTA extract. The taken-out soil was put into a beaker containing 400 mL of water, and was agitated by the same operation and frequency as the stirring in the EDTA extract and rinsed. FIG. 5 shows an operation flow.

3) Extraction method (mechanical stirring)
Implement 2 cases where soil A (200g) is put into a beaker containing 400mL of EDTA extract and stirred with a stirrer (200rpm) for 4 hours and 24 hours so that the ratio of soil to extract is 1: 2. did. After stirring for 30 minutes, the soil was taken out from the EDTA extract. The removed soil was placed in a beaker containing 400 mL of water, and rinsed while shaking the beaker a little to allow the entire soil to adjust to the water. As a control, the same procedure was used for the case where no EDTA extract was used (the extract was tap water only). FIG. 6 shows an operation flow.

(Experimental result)
Soil A Experimental Results Table 2 below shows the lead content and elution amount results of soil A after EDTA extraction treatment for each extraction method. In the immersion of the extraction method (1), the extraction rates after 4 hours and 24 hours were 20 and 32%, respectively. In the manual stirring of the extraction method (2), almost no extraction effect was observed with 5 stirrings, and the extraction rate was 27% after 10 stirrings. In the mechanical stirring of the extraction method (3), the extraction rates after mechanical stirring for 4 hours and 24 hours were 27 and 20%, respectively. The amount of lead elution after extraction was 0.18 and 0.097 mg / L after 4 hours and 24 hours in the extraction method (1), and 0.075 and 0.085 mg / L after 5 times and 10 times stirring in the extraction method 2, respectively. In the extraction method 3, after 4 hours and 24 hours, 0.074 and 0.082 mg / L, respectively, which were 74 to 180 times higher than the lead elution amount before the extraction treatment.

  By the way, it has been found that the solubility of heavy metals such as lead is greatly influenced by the presence (chemical) form of these heavy metals. Since EDTA chelates lead ions, the solubility of lead is thought to have a large effect on the extraction effect. Therefore, a sequential analysis by the Tessier method was performed on the presence of lead in soil A.

The results are shown in Table 3 below. As for the presence form of lead in soil A, the total of the exchange state and the carbonate bond state considered to be relatively highly soluble is about 25%, and the Fe-Mn oxide bond state and the organic matter bond state with low solubility. The mineral crystal lattice states were 46.5%, 12.7%, and 16.2%, respectively, for a total of 75.4%.

Soil B Experimental Results Table 4 below shows the lead content and elution amount results of soil B after EDTA extraction treatment in extraction method (1) and extraction method (3). The amount of lead elution after extraction is the result when the number of rinses in the extraction method (1) is set to 2 and the solid-liquid ratio of the rinse in the extraction method (3) is changed to 1: 5. It is. In the extraction method (1) immersion of 0.5 and 1 hour, almost no EDTA extraction was observed. In the mechanical stirring of the extraction method (3), the extraction rate was 29%, and an extraction rate comparable to that of the soil A was observed. The amount of lead elution after extraction is 0.051 and 0.068 mg / L after 0.5 hours and 1 hour respectively for extraction method (1), and 0.020 mg / L after 4 hours for extraction method (3). When the number of times of rinsing was set to 2 with respect to the previous lead elution amount, it was 51 to 68 times, and when the solid-liquid ratio was changed to 1: 5, the result exceeded 20 times.

(Discussion)
The presence form of lead in the soil A is about 25% in total in the exchange state and the carbonate binding state that are considered to have relatively high solubility, and the extraction method (the extraction operation is considered to be ideal by mechanical stirring) ( Considering that the extraction rate according to 3) is 20 to 27%, it is considered that the extraction of soil A by EDTA this time is mainly extracted with carbonate-bound lead. Therefore, it was confirmed that the extraction effect of EDTA is easily influenced by the presence form of lead (exchange state, carbonate binding state).

  In the extraction method (1), the extraction rates after 4 hours and 24 hours are 20 and 32%, respectively, and there is no significant difference from the extraction rate of the extraction method (3). The extraction limit is considered to have been reached. In the case of manual stirring in the pattern (2), the extraction effect is hardly recognized in the case of 5 times of stirring, and the extraction effect equivalent to the extraction method (3) is recognized in the case of 10 times of stirring, and a certain number of times of stirring is required. I understood.

  In order to verify the optimum soaking time in the extraction method (1), the extraction efficiency when soil B is used and the soaking time is shortened to 0.5 hour, 1 hour and so on is almost the extraction effect. Therefore, it was considered that an optimum soaking time of about 4 hours was necessary.

  The amount of lead elution from soil A after rinsing was significantly increased compared to before treatment. This is because a single rinse (solid-liquid ratio is soil A (200 g): rinse water (400 mL) = 1: 2) does not remove the EDTA adhering to the soil sufficiently, and the residual EDTA causes lead elution. The amount is thought to have increased.

  Then, when the result of the amount of lead elution by the difference in the solid-liquid ratio in the rinsing in the extraction method (3) of the soils A and B is seen, in the case of the soil B in which the amount of rinsing water is increased (solid-liquid ratio = 1: In 5), the lead elution amount was 0.020 mg / mL, and the lead elution amount decreased to about 1/4 of the solid-liquid ratio 1: 2 of the soil A rinse. Since soil A has a lead content 1.7 times greater than that of soil B, it cannot be simply compared, but it is thought that rinsing needs to take at least a solid-liquid ratio of 1: 5.

1) In extraction methods (1) to (3), the extraction efficiency by EDTA is about 30% at maximum. In addition, since the total of the ratio of the exchange state and the carbonate bond state of lead having a relatively high solubility is about 25%, it is considered that these forms are chelate-extracted, and the chelate extraction rate is It was found that the presence of lead is greatly affected.
2) It was found that in the immersion method (extraction method 1), the lead extraction rate was maximized after immersion for 4 hours or more, and was hardly extracted by immersion in a short time of 0.5 hour or 1 hour.
In addition, in manual stirring (extraction method 2), extraction was hardly performed in 5 times of stirring, and the extraction rate of lead was maximized in 10 times of stirring. It was confirmed that both immersion and manual stirring required a certain amount of immersion time and the number of times of stirring.
3) After extraction with EDTA, the amount of lead elution was greatly increased due to residual EDTA due to lack of rinsing. When the solid-liquid ratio of rinsing was increased to 1: 5, the amount of lead elution was reduced to about 1/4 of the solid-liquid ratio of 1: 2, so the solid-liquid ratio of rinsing was at least greater than 1: 5. I need to take it.

It is explanatory drawing which shows 1st Embodiment of the extraction method of the harmful heavy metals in the soil of this invention. It is explanatory drawing which shows the formation method of the water path which shows 2nd Embodiment of the extraction method of harmful heavy metals in the soil of this invention. It is a graph which shows the property of the lead pollution soil used in the experiment which confirms the effect of this invention. It is explanatory drawing which shows the operation flow of the immersion method among the experiments which confirm the effect of this invention. It is explanatory drawing which shows the operation flow of hand stirring among the experiments which confirm the effect of this invention. It is explanatory drawing which shows the operation flow of mechanical stirring among the experiments which confirm the effect of this invention. It is a flow block diagram which shows the soil washing | cleaning system in the purification treatment facility which processes pre-processed contaminated soil by a prior art example.

DESCRIPTION OF SYMBOLS 1 ... Soil bag 2 ... Tank 3 ... Contaminated soil 4 ... Cleaning liquid 5 ... Rinsing water 7 ... Pump 8 ... Permeable pipe

Claims (4)

(1) Put contaminated soil containing toxic heavy metals in a sandbag made of water-permeable material,
(2) Dipping the soil soil containing the contaminated soil into a tank containing a cleaning solution capable of extracting hazardous heavy metals from the contaminated soil for a certain period of time, and inserting a permeation tube into the soil soil, The washing water is sucked out and refluxed, and these are used to chemically extract and remove harmful heavy metals from the contaminated soil.
(3) As a result of the removal of toxic heavy metals in soil, the original contaminated soil that has been washed remains in the soil without flowing out of the soil, resulting in solid-liquid separation without special mechanical equipment. Extraction method.   The method for extracting toxic heavy metals in soil according to claim 1, wherein after immersing for a certain period of time, rinsing with tap water or water charged with a surfactant or the like is performed to remove the cleaning liquid remaining on the soil. The method for extracting toxic heavy metals in soil according to claim 1 or 2, wherein the sandbag is a large sandbag having a capacity of about 1 m ³ .   4. The method for extracting toxic heavy metals in soil according to claim 1, wherein the cleaning solution uses an acid extract such as hydrochloric acid, sulfuric acid or acetic acid capable of dissolving and extracting a chelating agent or heavy metals.

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