JP2005296941A - Method for cleaning lead-contaminated soil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively clean lead-contaminated soil through phytoremediation aiming at the cleaning with the use of a plant. <P>SOLUTION: Seeds or young seedings of a plant which are rich in oxalic acid are planted and grown in soil contaminated with lead and/or its compound. After allowing the plant rich in oxalic acid to absorb and accumulate lead and/or its compound, the plant is harvested and removed. As the plant rich in oxalic acid as described above, a plant belonging to the family Polygonaceae, Oxalidaceae, Chenopodiaceae, Araceae, Begoniaceae or Musaceae or a combination of the same is used. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for purifying lead-contaminated soil, particularly for purifying soil contaminated with lead, among methods (phytoremediation) for purifying soil contaminated with heavy metals by plants.

  In recent years, due to problems such as economic and environmental burdens, as a new soil contamination purification technology, plants that absorb and accumulate heavy metals in soil contaminated by heavy metals are grown, and these plants are harvested and removed to the environment. The technique (Phytoremediation) that attempts to remove heavy metals is attracting attention.

  For example, various phytoremediations shown in the following patent documents have been proposed.

  Patent Document 1 below proposes a purification method for cultivating a plant belonging to the genus Hyacinthaceae on a medium contaminated with heavy metals, absorbing and accumulating the heavy metals, and then harvesting the plants.

  In the following Patent Document 2, a plant belonging to the genus Akaza, Azaza, spinach, and Rhizobium is cultivated on a medium contaminated with heavy metals, and after the heavy metals are absorbed and accumulated, the plants are harvested. A purification method has been proposed.

  Patent Document 3 below proposes a purification method for cultivating a plant belonging to the genus Trolloaoi on a medium contaminated with heavy metals, absorbing and accumulating the heavy metals, and then harvesting the plants.

  In the following Patent Document 4, a soil purification method in which L-glutamic acid diacetic acid is allowed to coexist in the soil in a method for purifying the soil by absorbing heavy metals in the soil and accumulating them in the plant body. Has been proposed.

  In the following Patent Document 5, a method for purifying heavy metal-containing soil is proposed in which heavy metal-containing soil is planted in combination with at least two kinds of plants having the ability to absorb heavy metals and having different growth characteristics. Has been.

Furthermore, in the following Patent Document 6, a glycoside compound type plant (Aoki, Tade, buckwheat, assembly) or other compound type plant (Ache, fern) in soil contaminated with metals such as cadmium. In addition, a method for purifying contaminated soil has been proposed in which heavy metals in soil are removed by collecting and removing the plant from the soil after cultivating and growing to a certain extent.
JP 2002-332181 A JP 2002-331282 A JP 2002-336837 A JP 2003-275741 A JP 2001-276801 A JP-A-57-190 EDTA enhaned heavy metal phytoextraction: metal accumulation, leaching and toxicity (Plant and Soil 235: 105-114,2001 Enhancement of phytoextraction of Zn, Cd, and Cu from Calcareous Soil: The Use of NTA and Sulfur Amendments (Environmental Science & Technology 34,1778-1783,2000

  By the way, in recent years, lead contamination in shooting ranges has become a social problem. The lead content of the scattered lead shots eluted and caused soil contamination, and this lead component leaked into the river and the problem of contaminating living water became serious, and in some shooting ranges, lead removal There are many temporary closures.

  As a method for removing lead, for example, excavating contaminated soil and landfilling with soil (customer land reclamation method), solidifying the ground with cement-based solidification material and solidifying the lead component (soil improvement) Method), bioremediation using microorganisms, etc. are employed.

  However, in the case of the above-mentioned landfill method, it takes a lot of time and labor for excavation and landfill. In the case of the ground improvement method, there are problems that the soil environment changes greatly and the improvement work takes enormous costs and time. Furthermore, in the case of bioremediation using microorganisms, there are problems such as difficulty in managing microorganisms and low effectiveness in removing lead.

  On the other hand, in the case of phytoremediation for purifying contaminated soil with heavy metals by the plant, each of the methods disclosed in Patent Documents 1 to 6 can be considered promising for reasons such as low economic and environmental burdens. Phytoremediation is mainly intended for heavy metals such as cadmium and zinc. In particular, phytoremediation is not intended for removal of lead, and there is a problem that its removal effect is small for lead. For example, many plant species such as Gramineae, Asteraceae, and Leguminosae are used for purification of heavy metals, but lead absorption and accumulation are not observed in these plant species.

Lead has a large atomic weight among heavy metal elements and is a particularly heavy element among heavy metals, and has chemical characteristics that are difficult to dissolve in water under normal soil environmental conditions (physical and chemical conditions). The only lead-soluble salts that are soluble in water are lead nitrate (Pb (NO ₃ ) ₂ ) and lead acetate (Pb (CH ₃ COO) ₂ ). In the purification of heavy metals by plants, it is important to first change to a soluble form and absorb from the roots. However, when lead is the target, it is difficult to absorb from the plant roots due to the above chemical characteristics. No plant has been identified that selectively and effectively absorbs lead.

  On the other hand, in order to effectively absorb and accumulate heavy metals in plants, it is also performed to mix a chemical such as EDTA or citric acid into soil as a solubilization accelerator (see Non-Patent Documents 7 and 8 above). . However, artificially mixing these drugs into the soil, because EDTA has a slow biodegradability in the soil, it may remain in the soil for a long time and binds strongly to other cations, There is a risk of destroying the inherent function of the soil or changing its properties. In addition, since the amount of lead elution is increased several tens of times by spreading the chelating agent, there is a problem that lead contamination may be diffused if the wastewater treatment is mistaken.

  Therefore, the main problem of the present invention is to limit the removal target to lead and its compounds, and to obtain a remarkable lead removal effect by using a specific plant species, and to cause secondary contamination of the surrounding environment. The object is to provide a method for remediating lead-contaminated soil that is free from waste.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive research. As a result, plant species containing a large amount of oxalic acid, specifically, aceae, oxaceae, akazaceae, taroceae, euphorbiaceae, and salmonaceae The plant has obtained the knowledge that lead can be solubilized by organic acids such as oxalic acid secreted from the roots and effectively absorbed from the roots. The present invention is based on this finding.

  As a result, the present invention according to claim 1 is cultivated by sowing a plant species containing a large amount of oxalic acid in a soil contaminated with lead and / or a compound thereof, or transplanting young seedlings, Provided is a method for remediating lead-contaminated soil, characterized by absorbing and accumulating lead and / or compounds in a plant species containing a large amount and then harvesting and removing it.

  As the present invention according to claim 2, as the plant containing a large amount of oxalic acid, any one of a plant belonging to the family Taceae, Oleaceae, Rubiaceae, Taroceae, Scalyceae, Ganoderma is used in combination. A method for remediating lead-contaminated soil is provided.

  As described above in detail, according to the present invention, phytoremediation is performed using a plant species containing a large amount of oxalic acid, so that the lead component in the soil can be effectively absorbed from the root and removed from the soil. It becomes.

  Hereinafter, embodiments of the present invention will be described in detail.

  In this method of remediating lead-contaminated soil, sowing a plant species containing a large amount of oxalic acid (hereinafter referred to as a plant containing a high amount of oxalic acid) or transplanting a young seedling into soil contaminated with lead and / or a compound thereof. The plant species containing a large amount of oxalic acid is cultivated in accordance with the above, and after the lead and / or compound is absorbed and accumulated, it is harvested and removed.

Examples of the high oxalic acid-containing plants include podaceae plants represented by Inuta, Itadori, Gishigishi, oxalis plants represented by Oxalis, red crustaceae plants represented by Shiroza, spinach, taros, mulberry potatoes, etc. Can be used in combination with any one or a combination of the taroaceae plants, begonia, grove begonia, euphorbia, sempaflorences, and the like, or strelitzia, heliconia, basho, himebasho, ogibasho, etc. it can. The plant of the family Oxalidaceae and Polygonaceae contains about 10% or more of soluble potassium oxalate (potassium hydrogen oxalate KHC ₂ O ₄ ) in the whole plant. In addition, plants of the genus Chenopodiaceae contain 10% or more of soluble oxalic acid (sodium oxalate (CO ₂ Na) ₂ ).

  The soil to be applied is soil contaminated with lead and / or a compound thereof, specifically a shooting range.

  Oxalic acid and various organic acids (citric acid, malic acid, etc.) are generally known to be secreted from plant roots, and these organic acids all have a carboxyl group in the molecular structure. .

  In the present invention, lead and / or a compound thereof is made into a water-soluble form by oxalic acid secreted from a plant containing a high amount of oxalic acid, and is absorbed from the plant root and accumulated in the body. Compounds are removed from the soil.

  The above-mentioned oxalic acid-rich plant is cultivated for a period suitable for absorbing lead and / or its compounds, and the above-ground part of the plant including the stem and leaves or the underground root including the root is collected by an appropriate method. As a collection method, for example, a method of cutting only the above-ground part, and a method of collecting by repeatedly cutting when growing again, a method of cutting together the above-ground part of the plant and the underground root are arbitrary.

  The harvested plant is treated by incineration, pulverization, melting treatment, etc., and then lead is collected, or the incineration ash can be solidified and sealed with, for example, concrete or resin to make it harmless.

  By borrowing the temporarily closed dredging range, selecting a field where the lead content in the soil is relatively constant, plant species used in the purification method according to the present invention are the Japanese azalea (Turaceae), Itadori ( The plant group shown in Table 1 below is grown as a comparative example for 6 months, while the plant grows 5 species of (Taceae plant), Shigegi (Tapaceae plant), Oxalis (Oxaeaceae plant), and Shiroza (Acariaceae plant). Later, the aerial part and the underground root were harvested together and their lead content was examined.

  From the results of Table 1 above, it was found that the high oxalic acid content plant species used in the present invention has a significantly higher lead absorption / accumulation ability than other plants.

Claims (2)

  Soil contaminated with lead and / or its compounds is cultivated by sowing plant seeds rich in oxalic acid or transplanting seedlings, and lead and / or compounds are cultivated by planting seedlings rich in oxalic acid. A method for purifying lead-contaminated soil, characterized by harvesting and removing after absorption and accumulation. The method for purifying lead-contaminated soil according to claim 1, wherein the plant containing a large amount of oxalic acid is any one of or a combination of a plant belonging to the family Taceae, Oleaceae, Rubiaceae, Taroceae, Scalyceae, and Glyceae.