JP2004113858A - Method for cleaning harmful metal polluted soil by planting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a permanent cleaning means for soil polluted with a harmful metal such as heavy metals or the like or a harmful substance such as a radioactive substance or the like. <P>SOLUTION: Phytolacca americana L. Inb is planted in harmful metal polluted soil G and, after growth, the above-ground part thereof is removed from the planting soil to be subjected to harmful metal removal. Especially, a work period for removing the above-ground part from the planting soil is set to a floral bud forming period when a allelo-chemical compound (substance having allelopathy effect) A is discharged and the above-ground part, to which floral buds are formed, is removed at least once. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is a method of purifying land from harmful metal contamination by removing harmful metals from soil containing harmful metals, and more specifically, planting a plant having a high harmful metal accumulation ability on harmful metal contaminated soil, The present invention relates to a method for purifying toxic metal-contaminated soil by removing this plant from a planting site. Here, harmful metals are mainly heavy metals, but light metals and radioactive substances are also included in the sense that they are harmful to humans.
[0002]
[Prior art]
Soil pollution by toxic metals from industrial wastes is a serious problem. Development of a purification method for harmful and harmful metals present in soil is indispensable for preserving the environment of the next generation. Conventional purification methods include a method of insolubilizing harmful metals in contaminated land. This is to chemically adjust the contaminated soil by introducing chemicals and insolubilize and inactivate the harmful metal so that the harmful metal does not elute and diffuse from the contaminated soil to the surrounding environment. Although possible, soil toxic metals still exist. The harmful metal is once stabilized or non-eluted, but the soil itself may undergo a chemical change due to rainfall, oxidation, temperature change, etc. occurring in the course of time in the natural environment, and the harmful metal may be eluted again. This is not a permanent solution.
[0003]
There is also a method for removing contaminated soil from contaminated land. This requires enormous expense and labor, as a large amount of soil must be collected and transported, and is often a temporary measure only to relocate the contaminated soil removed to another location. Can cause similar pollution problems. This is not a permanent solution either. Therefore, there has been a demand for a permanent soil remediation method that removes only harmful metals selectively from contaminated soil, and in which the removed harmful metals do not become a new source of pollution. From this viewpoint, phytoremediation (soil remediation) by plants has been attracting attention since the 1970s, and various techniques have been proposed. (For example, see Patent Literature 1, Patent Literature 3, Patent Literature 4, Patent Literature 5, Patent Literature 6, Patent Literature 7, and Patent Literature 8.)
[0004]
Patent Literature 1 focuses on the fact that a specific plant can absorb heavy metal and accumulate it in a large amount. Such a plant is planted in a soil contaminated with heavy metal, and the mechanism of absorption and accumulation of heavy metal is considered. In particular, a larger amount of heavy metal is accumulated in the roots, which are underground parts than the above-ground parts such as plant stems and leaves, and not only ionized heavy metals but also heavy metals that exist as stable compounds are ionized and absorbed. Is described. In addition, as plants having high heavy metal accumulation ability suitable for purification of soil contaminated with heavy metals, there are Asteraceae, Ossilophilaceae, Lamiaceae, Legumes, Solanaceae, Hanashinobaceae, Liliaceae, Craneaceae, Rosaceae, Rhododendronaceae, Hypericumaceae, and Laceae. , One of the following species: Cypress family, Cypress family, Berberaceae family, Birch family, Myrtaceae family, Apocynaceae family, Saxifragaceae family, Grass family, Iridaceae family, Cannaceae family, Convolvulaceae family, Brassicaceae family, Mesidae family, Akaza family, Aceraceae family, Salix family It is described as the above plant.
[0005]
However, in these preferred plants, the ability to accumulate harmful metals, including heavy metals, is not very high. Specifically, the harmful metal to be purified is less than 5 ppm when measured by the dry weight of each plant. In addition, experiments have been shown to prove the above description that "a large amount of heavy metal is accumulated in roots" and "Ionize and absorb not only ionized heavy metals but also heavy metals existing as stable compounds". Questions about reproducibility and practicality.
[0006]
Other Patent Documents 3, 4, 5, 6, 7, and 8 have not proposed a plant having an effective purification action enough to be put to practical use as a soil pollution purification method. In addition, a part of the patent document proposes a complicated and costly method of forming hairy roots having a remarkable purifying effect by introducing a plasmid of hairy root disease fungus, or improving the purifying ability by transformation by gene introduction. Yes, but there is doubt about its practicality.
[0007]
On the other hand, Patent Document 2 describes utilization of allelopathic action of a plant, which releases an allelopathic substance having a herbicidal effect and provides a stable transgenic plant. The issue is not to purify metal-contaminated soil.
[0008]
“Allelopathy” is translated as “allelopathy” and its definition is that “a chemical released from a plant exerts some inhibitory or promoting action on other plants, microorganisms or insects. Phenomenon. Examples include chemicals released by the valerian grassland in vacant lots and fallow land, which control the growth of other plants, legume pasture "Hairy Vetch" to control weeds in orchards and fallow land, and the native Japanese bean "Hasomame". Weed control and insect pest control, "Hambana" rodents, moles, and pest control, "buckwheat" weed control, and weed control by tree fallen leaf cover. In addition, there is a research report that caffeine contained in a large amount in coffee and tea significantly inhibits germination of plants other than legumes, and this is also said to be a type of allelopathy. At present, research is being conducted on the use of this allelopathy to exterminate grass with grass. A weed control method that suppresses only specific weeds and does not harm crops has an advantage that it is less effective than the use of herbicides but has less effect on the environment.
[0009]
Non-Patent Document 1 describes the problem of phytoremediation (soil remediation) using plants, and there is no specific description of such a method. Non-Patent Document 1 reports that the pokeweed (ink-berry) used in the present invention is a plant that accumulates rare earth elements, but does not suggest use for soil contamination. Non-Patent Document 3 describes the correlation and proportional relationship between elements contained in mugwort and growing soil, and Non-Patent Document 4 uses the element content of plants such as mugwort as an indicator (standard) of soil contamination. No description is given in detail about the purification of toxic metal-contaminated soil.
[0010]
[Patent Document 1]
JP 2000-288529 A [Patent Document 2]
JP-A-10-150983 [Patent Document 3]
JP-A-57-190 [Patent Document 4]
Japanese Patent Publication No. 7-508206 [Patent Document 5]
Japanese Patent Application Laid-Open No. 2000-167534 [Patent Document 6]
JP 2000-176433 A [Patent Document 7]
JP 2001-275683 A [Patent Document 8]
JP-A-2002-172380 [Non-Patent Document 1]
Cunningham, S.M. D. , Betri, W.C. R. Huang, J .; W. (1995), Trend Biotech, vol 13, p 393-397.
[Non-patent document 2]
Ichihashi, H .; , Morita, H .; Tatsukawa, R .; (1992), Envoiron. Polut. , Vol76, p157-162
[Non-Patent Document 3]
Honma, S.M. Tsumita, K .; . , Shirata, K .; (1977), Envoiron. and Human Surval. Ministry of Education. p103-111
[Non-patent document 4]
Baker, A .; J. M. McGrath, S .; P. Reeves, R .; D. , Smith, J.M. A. C. (1999), Metalhyperaccumulator plants, p85-107.
[0011]
[Problems to be solved by the invention]
The present invention is a method for purifying land from harmful metal contamination by removing harmful metals from soil containing harmful metals, and is basically harmful to harmful metal-contaminated soil containing harmful metals described in Patent Document 1. The object of the present invention is to solve a problem relating to a method for purifying toxic metal-contaminated soil in which a plant having a high metal accumulation capacity is planted, and then the plant is removed from the planting site. Specifically, a suitable species of such a plant to be planted is specified, and a suitable planting method and a suitable removal method are provided.
[0012]
[Means for Solving the Problems]
The present invention provides a method for purifying a toxic metal-contaminated soil, in which a plant having a high toxic metal accumulation ability is planted in the toxic metal-contaminated soil, and then the plant is removed from the planting place. The planted plant is Phytolacca americana ), The above-ground part of the pokeweed is removed from the planting ground, and the removed part of the pokeweed is treated with harmful metals. That is, the inventor has suggested that the plant plant suitable for solving the problem is the pokeweed pokeweed, and not the entire pokeweed poke but the above-ground part is removed from the planting ground, and the removed pokeweed pokeweed is treated with harmful metal. I found out what to do.
[0013]
In this project, only the above-ground part of the pokeweed is removed from the planting ground, and the terrestrial part of the removed pokeweed is treated with harmful metals. Of course, the harmful metals are also absorbed in the roots of the pokeweed, so removing the entire pokeweed in the short term will remove more harmful metals. However, as described later, in pokeweed pokeweed, harmful metals absorbed from soil tend to translocate from roots to stems to leaves. With. Moreover, if the roots are left, the above-ground parts (stems and leaves) will be regenerated, and there is no need to plant again.
[0014]
The pokeweed has a long (deep) root of about 1 m. This has the advantage that harmful metals in deeper parts of the land can also be absorbed. The pokeweed pokeweed is often found in slightly open areas, such as in open areas, wastelands, riverbanks, and bamboo forests. The flowers are pale-purple, whitish flowers, and in summer, they often become ears. From that time on, the whole grass began to grow and in the fall it became a 1-2 meter tall plant. Then, black-purple fruits having a diameter of about 8 mm are conspicuous. It is a naturalized plant native to North America that was introduced around the beginning of the Meiji era and has increased in various parts of the country. Josh is a Western species and its name is derived from its roots resembling pokeweed. There is also an alias for American pokeweed bearing the name of the place of origin. When this fruit is crushed by hand, the dark purple-colored juice gets on the hand. In its place of origin, it is called an ink-berry.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
It is important to utilize plant allelopathy in the practice of the present invention. After studying the planting of the pokeweed over a long period of time, it was found that the first generation pokeweed was grown and then the second generation pokeweed was planted. We believe that the reason is allelopathic action by the pokeweed. Like the general allelopathic effect, the allelopathic effect of Pleurotus pokeweed has not been elucidated scientifically, but it is experimentally clear that the first-generation planting has a promoting effect on the second-generation homologous growth. Therefore, when purifying toxic metal-contaminated soil, it is preferable to plant the pokeweed a plurality of times.
[0016]
By planting the perennial pokeweed for several years, a plant allelopathic effect can be obtained. Here, it is desirable to reap the above-ground parts as often as possible. The standard for this cutting is the time of flower bud formation. At that time, the growth of biomass stops, and by cutting the above-ground part, the release of allelochemicals (substances having an allelopathic effect) from the roots is increased, and contaminant metals are reduced. This is because it is considered to be easier to absorb. In other words, in the most orthodox state, it is planted and left for two years or more to absorb harmful metals and synergistically increase the allelopathic effect. Furthermore, in order to activate allelopathy, it is preferable to cut down the above-ground parts frequently at the time when flower buds are formed.
[0017]
FIGS. 4, 5, and 6 illustrate the above operations. FIG. 4 (a) shows a plant in which a pokeweed Inb is planted on soil G contaminated with harmful metals, which grows as shown in FIG. 4 (b) and gives buds as shown in FIG. 5 (c). By this time, allelochemicals (substances having an allelopathic effect) are released from the roots to some extent, and the release of allergic chemicals is further enhanced by removing the above-ground parts (FIG. 5 (d)). Therefore, as shown in FIG. 6E, the pokeweed pokeweed Inb2 is planted in the gap between the pokeweed pokeweed Inb1 planted the first time. Thereafter, as shown in FIG. 6 (f), the above-ground part is cut off and treated with harmful metals at the time when it has grown and formed flower buds.
[0018]
Further, when planting pokeweed on the soil to be purified, it is preferable to mix natural soil before planting or during the planting operation because the growth of pokeweed is promoted. The cause is also considered to be allelopathic action by the natural soil itself or any plant-derived substance mixed into the natural soil. The natural soil to be mixed is preferably the natural soil of the land where the pokeweed grows. The amount of the natural soil mixed is effective at about 7 to 8% of the weight of the soil for burying roots used for planting the roots of the pokeweed.
[0019]
That is, at the time of planting, iodine is mixed with a toxic metal-contaminated soil temporarily removed to fill the rhizome of the pokeweed and other soil having a weight of one-tenth or less of the weight of the removed soil. It is preferable to bury the rhizome of the pokeweed for planting. Further, it is preferable that the other soil is soil of a land where a plant of the pokeweed pokeweed naturally grows. The reason for this is considered to be allelopathic action by the same species growing soil, or the fact that the soil, which is a natural growth environment, contains trace elements suitable for growing pokeweed.
[0020]
In addition, the pokeweed to be planted is naturally grown on soil containing the harmful metal to be purified at a concentration of 0.1 ppm or more and cultivated on the soil containing the harmful metal to be purified at a concentration of 0.1 ppm or more. , The harmful metal to be purified is well absorbed. This is considered to be one expression of adaptation to the growth environment. A scientific explanation of this phenomenon is not yet available.
[0021]
The determination of soil containing harmful metals to be purified at a concentration of 0.1 ppm or more may be performed by ordinary soil analysis, or the harmful metals to be purified may be determined using soil monitoring species such as Hebinonekoza, Ragweed, and Artemisia. It may be obtained indirectly from the amount of harmful metal contained in the metal. Of course, pokeweed may be used as a soil monitoring species.
[0022]
Further, it is preferable that the pokeweed to be planted contains 1 ppm or more of a harmful metal to be purified by dry weight. In other words, the pokeweed pokeweed, which originally contains harmful metals in its environmental soil, has a high ability to absorb harmful metals. In addition, those in which the burdock burdock itself contains a harmful metal are evidence that the ability to absorb harmful metals is high. The production area of the pokeweed to be planted may be selected based on these criteria.
[0023]
FIGS. 1, 2 and 3 are drawings of the abstracts of "Possibility of monitoring and repairing trace metal element contamination using pokeweed" released at the Society of Environmental Chemistry. These supplement the explanation of the present invention. FIG. 1 shows a measurement example of the plant species and the amount of Cd accumulation (a plant collected in Annaka City), and it can be seen that Phytolaccaseae, which is a kind of pokeweed, is an outstanding Cd accumulation amount compared to other species. FIG. 2 shows the relationship between the locality of the pokeweed and the accumulated amounts of Tl (thallium) and Be (beryllium), which are extremely large in those collected at the contaminated area of Dajin-shan, Shanghai, China. You can see that it is done. FIG. 3 is a diagram (Spearman's rank correlation) showing a correlation between soil Cd and Zn concentrations and amounts of Cd and Zn contained in roots, stems and leaves of the pokeweed. There is a correlation with the soil concentration, suggesting that Cd and Zn tend to translocate from root to stem to leaf.
[0024]
Supplementary examples of harmful metals. Regarding the toxicity of cadmium Cd (atomic number = 48), it is common in cadmium poisoning called itai-itai disease in the Jinzu River basin in Toyama Prefecture. This is a kidney in which cadmium accumulates, and cadmium inhibits the function of zinc enzyme from its similarity as an element, causing renal damage. Beryllium (Be) belongs to a light metal (atomic number = 4), and its compound is sweet and highly toxic. It is so toxic that even small quantities can be fatal, but the reasons for its toxicity are not fully understood. Thallium (Tl) (atomic number = 81) is one of the most toxic elements. In the past, thallium sulfate was used to control ants and rats, but humans have no taste or smell. Since the lethal dose of the substance was very dangerous, about 2 g, it was no longer used.
[0025]
Furthermore, if the pokeweed is planted even in soil contaminated by radioactive substances, the radioactive elements are absorbed by the pokeweed (data not shown). By utilizing this to plant pokeweed, it is possible to safely and reliably treat radiation-contaminated soil, although the period is long.
[0026]
The removed plants are incinerated at 900 ° C. or higher using a sealed incinerator having a high-temperature treatment section formed by electricity, plasma, or general fuel energy. This is a known method for treating harmful metal-containing substances. The closed-type incinerator is a generic name for incinerators having a structure in which incineration fly ash and volatile harmful metals do not leak to the outside world as much as possible. Any incinerator may be used as long as it is such an incinerator. After incineration, spontaneous cooling may be performed up to about 500 ° C., but at least in the range of 300 to 450 ° C., do not stay for a long time in order to prevent generation of dioxin. Desirably, rapid cooling is performed in this range. The incineration ash is taken out when the furnace temperature reaches room temperature or several tens of degrees. Further, when incineration residues such as dust are attached to the furnace wall or the like, it is preferable to take out the incineration residue at the same time, combine it with incineration ash to make incineration, and perform the following treatment.
[0027]
Since the incinerated material taken out is considerably reduced in volume, for example, a known inorganic solidifying material such as a cement-based solidifying material is added to solidify to make it difficult to elute harmful metal components, and the solidified material is disposed of in landfill. You can also. It is also preferable to separate and collect the harmful metal components concentrated in the incineration, and reuse the collected harmful metals as valuable resources. The separation and recovery of harmful metals in the incineration ash may be performed by any known method. For example, a method is commonly used in which incinerated ash is acid-washed with sulfuric acid or hydrochloric acid to elute harmful metals, and a liquid obtained by solid-liquid separation of the ash is subjected to alkali treatment to precipitate harmful metals as a high-purity compound. It is a target.
[0028]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, since a harmful metal component can be efficiently removed from the soil contaminated with the harmful metal, it can take time, but can regenerate the soil to the soil from which the harmful metal has been eliminated. Removal removes only the above-ground parts regularly and leaves the roots intact. The above-ground part will be regenerated and the absorption will be permanent, so once planting it is only necessary to cut the above-ground part regularly. Moreover, since the roots are deep, it is possible to remove harmful metals about 1 m below the ground surface.
[Brief description of the drawings]
Fig. 1 Plant species and Cd accumulation (plants collected in Annaka City)
[Fig. 2] The locality of the pokeweed and the accumulation of TI (thallium) and Be (beryllium). [Fig. 3] Diagram showing correlation (Spearman's rank correlation)
FIG. 4 is an explanatory view of a pokeweed planting of the present invention, part 1
FIG. 5 is an explanatory view of the pokeweed planting of the present invention, part 2
FIG. 6 is an explanatory diagram 3 of the pokeweed pokeweed planting of the present invention.
[Explanation of symbols]
A Allelochemicals released from roots (substances with allelopathic effect)
Be Beryllium Cd Cadnium F Flower bud G of pokeweed G Soil contaminated with harmful metals Inb pokeweed (ink-berry)
Inb1 The first planted pokeweed (ink-berry)
Inb2 The pokeweed (Ink-berry) planted the second time
Tl thallium

Claims (7)

In a method for purifying harmful metal-contaminated soil by planting a plant having a high harmful metal accumulation ability on the harmful metal-contaminated soil, and then removing the plant from the planting ground, the plant is a pokeweed pokeweed, Of harmful metal-contaminated soil by removing the above-ground part of the plant from the planting ground and treating the removed part of the pokeweed burdock with harmful metal The harmful metal according to claim 1, wherein the operation of removing the above-ground portion from the planting place is at the time of flower bud formation of the pokeweed, and at least once removing the above-ground portion where the flower bud is formed. How to clean contaminated soil In the planting according to claim 1 or claim 2, the harmful metal-contaminated soil temporarily eliminated to fill the rhizome of the pokeweed and other ones having a weight of one tenth or less of the weight of the eliminated soil. A method for purifying toxic metal-contaminated soil by burying the rhizome of the pokeweed and planting it with a mixed soil mixed with soil A method for purifying toxic metal-contaminated soil, wherein the other soil according to claim 3 is a soil of a land where a plant of the pokeweed plant to be planted naturally grows. The pokeweed to be planted according to any one of claims 1 to 4, wherein the harmful metal to be purified is naturally grown or 0.1 ppm or more in the soil containing the harmful metal to be purified at a concentration of 0.1 ppm or more. Of Hazardous Metal Contaminated Soil Cultivated on High Concentration Soil A method for purifying harmful metal-contaminated soil, wherein the pokeweed to be planted according to any one of claims 1 to 4 contains a harmful metal to be purified in an amount of 1 ppm or more by dry weight. The plant according to claims 1 to 4, wherein the pokeweed is planted on the toxic metal-contaminated soil in two stages, and after the first planting, The above-ground portion of the first planted pokeweed which had flower buds formed at the time of flower bud formation was removed at least once, and the second time in the planting gap of the first planted pokeweed after the removal operation. Of harmful metal-contaminated soil that is planted

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