JP2005279637A - Method for removing and recovering heavy metal in soil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for removing and recovering heavy metals in soil by phytoremediation having an improved removal and recovery ratio of the heavy metals in soil by choosing a plant which highly absorbs the heavy metals and has high harvesting amount and many annual cultivation frequency and establishing cultivation technique for improving absorption of heavy metals. <P>SOLUTION: A plant belonging to the genus Avena strigosa is cultivated on the soil to absorb and accumulate the heavy metals in soil and then the plant is harvested to recover the heavy metals in soil. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a phytoremediation method, and more particularly, to a method for removing and recovering heavy metals in soil using a plant belonging to wild wheat seeds.

  Conventionally, in order to repair contaminated soil with cadmium (Cd) and the like, civil works such as soil removal and customer soil have been carried out. However, since this method has a high cost and a problem in disposal of soil that has been discharged, new technological development is required. As one of the solutions, a technique called “phytoremediation method” in which heavy metals such as cadmium in soil are removed by plants has been reevaluated.

  Phytoremediation is a remediation method (pollution purification / repair method) that uses the ability of plants to accumulate and decompose environmental pollutants. Here, phyto means a plant.

  Specifically, it is a method of removing harmful substances from soil and groundwater by utilizing the ability of plants to absorb moisture and nutrients from roots. Alternatively, there is a method of purification by joint work with rhizobia and microorganisms (decomposing microorganisms: soil bacteria such as phenol-utilizing bacteria) that form the rhizosphere.

  These include cases where pollutants are decomposed by the action of the body of the plant and microorganisms and cases where they are absorbed and concentrated in the body of the plant. The substance can be removed. In the case of heavy metals, not only can contamination be removed, but concentrated heavy metals can be extracted and recovered, and heavy metals can be recycled.

As such a phytoremediation method, for example, there is a method in which a heavy metal plant is cultivated in a target soil such as kenaf and the plant is made to absorb a heavy metal, and then the plant is harvested (for example, , See Patent Document 1).
JP 2002-332181 A

  However, while this phytoremediation method can remove cadmium and the like at a low cost, the biggest problem is that the removal speed is slow.

  In addition, in the purification method according to Patent Document 1, kenaf is a tropical plant, so the seeding time is from late April to around June, and it cannot be cultivated in the fallow season (back cropping) in autumn and winter. there were.

  Therefore, in order to develop and put into practical use efficient purification technology for heavy metal-contaminated soil by plants, (1) in conjunction with the selection of plants that highly absorb heavy metals, the cultivation technology for increasing absorption and the system for increasing yield technology. There is an urgent need to resolve issues such as establishment, (2) establishment of efficient harvesting technology for cultivated plants, and (3) establishment of safe and efficient treatment methods for harvested crops.

  The present invention is a plant that absorbs heavy metals in the light of the above-mentioned problems of the prior art, and by selecting a plant with a high yield and annual number of cultivations and establishing a cultivation technique for increasing the absorption of heavy metals. An object of the present invention is to provide a method for removing and recovering heavy metals in soil by phytoremediation with improved removal and recovery of heavy metals in soil.

To solve this problem,
The invention according to claim 1 cultivates a plant belonging to the grass family Avena trigosa in soil, absorbs and accumulates heavy metals in the soil, harvests the plant, A method for removing and recovering heavy metals in soil, characterized by recovering heavy metals therein.

  The invention according to claim 2 is the removal and recovery of heavy metals in soil according to claim 1, wherein the plant is one or more selected from the group consisting of Avena trigosa Screb., Hey Oats, and New Oats. Is the method.

  Invention of Claim 3 is the removal and collection | recovery method of the heavy metal in a soil of Claim 1 or 2 which grows the said plant in the said soil whose pH is 4.5-7.5.

  The invention according to claim 4 is the method for removing and recovering heavy metals in soil according to any one of claims 1 to 3, wherein the heavy metal in the soil is zinc, cadmium, or a compound containing these metals. It is.

  In the invention according to claim 5, after harvesting the plant, the plant is supplied into a smelting furnace used for zinc smelting, and zinc and / or cadmium is recovered in the process of zinc smelting. 5. The method for removing and collecting heavy metals in soil according to any one of 4 above.

  According to the method for removing and recovering heavy metals in soil of the present invention, by using a plant belonging to wild wheat seeds, high absorption of heavy metals is possible, and the removal and recovery rate of heavy metals in soil becomes phytoremediation. .

  Moreover, according to the method for removing and recovering heavy metals in the soil of the present invention, by using a plant belonging to the wild oat species, the yield is large, and since it can be cultivated many times a year including autumn and winter, the soil The removal / recovery rate of heavy metals can be improved.

  Furthermore, according to the method for removing and recovering heavy metals in the soil of the present invention, by cultivating a plant belonging to the wild oat species as fallow or a reverse crop, the plant belonging to the wild oat species can increase the density of plant parasitic nematodes in the soil. In order to reduce, it is possible to remove and collect heavy metals in the soil and to suppress damage to the surface crops by plant parasitic nematodes.

  The method for removing and recovering heavy metals in soil according to the present invention comprises cultivating a plant belonging to the genus Avena trigosa in the soil, absorbing and accumulating the heavy metal in the soil, Harvesting and recovering heavy metals in the soil.

  The plant used in the present invention is a plant that belongs to the grass family Avena trigosa. The oat is a plant belonging to the genus Oataceae, the subfamily Odonaceae, and the cultivars include cultivated species (Avena sativa L.) and wild species (Avena trigosa and Avena trigosa Screb.). Oat cultivation species are cultivated for feed and include Amuri II, Advance, Super Hayate, Endax, etc. by variety name.

  On the other hand, wild oat species are generally known as green manure crops and are used as control crops that reduce the density of plant parasitic nematodes in the soil. Among these, at least one selected from the group consisting of Avena trigosa Screb., Heavens (Avena trigosa), and New Oates (Avena trigosa) is preferable, and Negusa retage is more preferable. Table 1 shows the general characteristics of these three varieties.

  In Table 1, ◎ means optimal, ○ means appropriate, and × means inappropriate. Cultivars with excellent cold resistance and acidity can be cultivated in cold regions and acidic soils.

  The soil which is the subject of the present invention is the soil of all land such as agricultural land, industrial land, urban area, residential area and the like. It may be soil such as a factory site that is artificially contaminated with heavy metals at high concentration, or may be soil such as natural contaminated farmland.

  The soil properties of the soil are preferably sandy loam soil, loam soil, loam soil, and dredged soil from the viewpoints of drainage, water retention, nutrient retention, nutrient content, and root group elongation.

Moreover, the heavy metal in the soil in the present invention includes metal species that are problematic as heavy metal contamination such as cadmium, zinc, lead, copper, mercury, and compounds containing these metals. Among these, cadmium, zinc, or a compound containing these metals is preferable.
The target soil may or may not contain any metal other than the heavy metal.

In order to cultivate the plant in the soil, the soil as it is may be used, or the soil environment may be modified using a soil improvement application material or a fertilizer if necessary.
As such an application material, water-soluble salts such as ammonium, potassium, phosphoric acid, calcium, magnesium, and sodium can be applied.

  Specifically, ammonium chloride, ammonium sulfate, ammonium phosphate, ammonium acetate, ammonium nitrate, potassium chloride, potassium sulfate, potassium sulfate clay, potassium silicate, ethylenediaminetetraacetate potassium, oxalate potassium, potassium citrate, superphosphate Lime, molten phosphorus fertilizer, heavy superphosphate lime, calcium chloride, calcium sulfate, calcium hydroxide, calcium carbonate, calcium nitrate, quicklime, calcium acetate, calcium citrate, calcium ethylenediaminetetraacetate, magnesium chloride, magnesium carbonate, silica Compound fertilizer and advanced chemical fertilizer containing magnesium acid, magnesium ethylenediaminetetraacetate, sodium chloride, sodium oxalate, sodium citrate, sodium ethylenediaminetetraacetate, nitrogen, potassium, phosphorus, etc. Nitrogen, and a blend fertilizer containing potassium.

  Among these, potassium chloride is preferable from the viewpoint of solubilizing cadmium that is substituted and adsorbed on clay in the soil.

  Such an applied material may be given to plants as a basic manure or may be given as additional fertilizer. By giving potassium chloride as additional fertilizer, absorption of cadmium and zinc to plants belonging to wild wheat seeds can be promoted. In addition, regarding the absorption of cadmium and zinc into plants belonging to the wild oat species, as the amount of cadmium absorbed increases, the amount of zinc absorbed also tends to increase.

  In order to remove and recover heavy metals from the soil, methods for cultivating the plant used in the present invention include methods by outdoor cultivation sowing directly to the soil at an appropriate time, seedlings by seedbeds, seedlings by seedling boxes, cell seedlings And a method of transplanting seedlings grown in a form suitable for cultivation such as pot seedlings, plug seedlings, and paper pot seedlings, or vegetatively propagated plants. And according to the state of a plant and contaminated soil, these methods can be taken arbitrarily.

  Moreover, the pH of the soil which grows the said plant is 4.5-7.5, Preferably 4.8-6.5, More preferably, the range of 5-6 is suitable. In particular, cadmium is easily eluted from soil when the pH of the soil is on the acidic side, so dilute hydrochloric acid, dilute sulfuric acid, ferric chloride, sulfate, etc. are added to make the pH of the soil acidic within a range that does not contaminate the environment. It is preferable to adjust to the side. Plants belonging to wild oat species are strong in acidity, and therefore can be cultivated even in such acidic soil.

  By growing the plant belonging to the wild barley species with a soil pH of 4.5 to 7.5, cadmium is easily absorbed by the plant, so that the removal rate of heavy metals, particularly cadmium, can be improved.

  The plant in the present invention is cultivated for a period suitable for absorbing heavy metals. The time for growing the plant can be arbitrarily set according to the cultivation conditions and the like. Unlike tropical plants such as kenaf, plants belonging to the wild oat species used in the present invention can grow even at low temperatures, so not only from spring to summer, from summer to autumn, but also from autumn to spring. It can also be cultivated during the fallow season.

  Moreover, since the plant belonging to the wild oat species can be sufficiently harvested even in the cultivation period of about 2 months, cultivation can be repeated many times a year. By increasing the annual number of cultivations of plants belonging to the wild oat species, the removal rate of heavy metals in the soil can be further improved.

After the heavy metal in the soil is absorbed and accumulated in a plant belonging to the wild barley species, the above-ground part of the plant body including stems and leaves and / or the below-ground part of the plant body including roots is harvested by an appropriate method. Among them, from the viewpoint of increasing the heavy metal removal and recovery rate, it is preferable not only to cut the above-ground part but also to dig up and harvest the roots.
Moreover, this absorption and accumulation period can be changed according to cultivation conditions, soil conditions, the amount of heavy metals that can be absorbed, and other conditions.

  Further, harvesting may be performed in a state of green cutting, or may be performed after the plant is withered and dried. Among them, it is preferable to harvest by cutting blue before heading from the viewpoint of preventing the return of heavy metals to the soil due to falling ears. The term “green cutting” refers to collecting a plant before the fruit ripens.

  As described above, plants belonging to wild oat species are generally known as green manure crops. However, in the present invention, heavy metals in soil are absorbed and removed / recovered by plants belonging to wild oat species. In order to do so, it will not be used as green manure after being harvested.

  The amount of heavy metal absorbed by the plant is measured for each part of the above-ground part of the plant body or the underground part of the plant body after the plant is harvested and dried. First, each part is decomposed with a mixed acid of nitric acid and perchloric acid, the residue is filtered and then prepared as a sample solution, and an analysis method such as a high frequency inductively coupled plasma emission analysis (ICP-AES) method or an atomic absorption method (AAS) Can be used to measure the concentration of heavy metals.

  Harvested plants concentrate, extract and collect accumulated heavy metals. Examples of the treatment for concentrating heavy metals include drying treatment, incineration, pulverization, melting, decomposition by microorganisms, decomposition treatment by a method such as composting. Among these, a method of supplying this plant into a smelting furnace used for zinc smelting and recovering zinc and / or cadmium in the process of zinc smelting is preferable from the viewpoint of cost and heavy metal recovery rate.

  FIG. 1 is a process diagram showing an example of a zinc smelting method used in the zinc and / or cadmium recovery method according to the present invention.

  In the smelting method shown here, first, zinc concentrate (metal raw material), which is a zinc raw material, is roasted in a roasting furnace, which is a smelting furnace, to produce a sinter. As such a roasting furnace, a wedge roasting furnace, a flash roasting furnace, or a fluid roasting furnace can be used. At this time, a part of zinc sulfide in the zinc concentrate is oxidized by roasting to become zinc oxide. Moreover, it is preferable that the temperature in a roasting furnace shall be 880-930 degreeC.

  The sulfur concentration in the sinter is preferably 1-2% by mass. Moreover, it is preferable to grind | pulverize a thing with a big particle size among baked ores, and to supply a roasting furnace again.

  The harvested plant belonging to the wild oat species is fed into the roasting furnace together with the zinc concentrate in this step. The plant is preferably dried in advance. In this step, the organic matter contained in the plant supplied into the roasting furnace is thermally decomposed, and a burned ore containing heavy metals absorbed and accumulated from the soil is obtained.

  Further, when a plant belonging to the wild oat species is supplied into the roasting furnace, it is supplied so as to cover at least a part (preferably almost the entire surface) of the zinc concentrate surface (upper surface) in the roasting furnace. Is preferred. By performing this operation, the zinc concentrate can be kept warm, the heating efficiency of the roasting furnace can be increased, and the heating cost can be reduced.

Next, the sinter is leached using an electrolytic tail solution (sulfuric acid or the like) described later in a neutral leaching tank, and then processed into a neutral solution that is a leaching solution containing zinc. Examples of the treatment method include a single leaching method, a double leaching method, and a reverse leaching method.
In this step, Fe is oxidized using MnO ₂ and precipitated as Fe (OH) ₃ , and As and Sb are also co-precipitated, and these are removed together with the dissolved residue by filtration.

  Next, the neutral liquid (zinc-containing leachate) obtained in the leaching step is supplied to the first liquid purification tank. Zinc powder, arsenous acid, and the like are added to the first liquid purification tank, and impurities such as Cu, Ni, and Co in the neutral liquid are removed as the first liquid residue.

Then, the neutral liquid which passed through the 1st liquid tank is supplied to the 2nd liquid tank. To this second liquid tank, zinc powder is further added, and cadmium is substituted and deposited as a second liquid residue.
In addition, although the liquid purification process which has a two-stage process (1st and 2nd liquid tank) here was illustrated, a liquid purification process is good also as three or more steps.

  The second purified liquid residue containing the deposited cadmium is sent to the cadmium smelting process, and cadmium is recovered from the second purified liquid residue. A conventionally well-known method can be used for smelting of cadmium.

  On the other hand, the purified solution that has passed through the second purified solution tank is supplied to the electrolytic cell, and zinc is electrolyzed. The obtained electrolytic zinc is melted in a low frequency electric furnace, and zinc is recovered. At this time, the electrolytic tail solution (such as sulfuric acid) used in the electrolytic tank is supplied to the neutral leaching tank in the leaching step and reused.

  According to the above zinc and / or cadmium removal and recovery method, plants belonging to the wild oat species are supplied to a roasting furnace, and in the smelting process (roasting, leaching, liquid purification, zinc smelting, cadmium smelting) Since zinc and / or cadmium is removed and recovered, the existing smelting method can be used as it is, and zinc and / or cadmium can be easily removed and recovered at low cost.

  In addition, since a large part of the cadmium derived from the raw material (zinc concentrate) passes through the sinter, neutral liquid, and moves to the purified liquid residue, the above plant is supplied to the zinc smelting process. Cadmium can be recovered together with cadmium derived from the raw material (zinc concentrate).

  In addition, since it is possible to recover zinc and / or cadmium derived from plants belonging to wild oat species by such a simple operation, the recovery cost of zinc and / or cadmium is suppressed and the recovery rate of these is increased. Can do.

  Hereinafter, the present invention will be described in more detail by way of examples. The present invention is not limited to the following examples.

[Example 1]
500 g / 5 m ^{2 of} urea sulfide phosphorous acid 48 was applied to loam soil (base substitution capacity 11-13 me / 100 g) complex-contaminated with heavy metals, and plowed. The heavy metal content in the soil was measured using an atomic absorption spectrometer (manufactured by Nippon Jarrell Ash Co., Ltd.). As a result, cadmium 3.88 mg / kg, zinc 950 mg / kg, copper 100 mg / kg, lead 130 mg / kg.

The plowed soil was seeded with 50g / 5m ² of wild oat cultivar (Avena trigosa Screb.) In the beginning of October and subjected to normal cultivation management (open field cultivation, natural drainage). The fertilizer is divided into the case where only urea urea sulfide No. 48 500 g / 5 m ² is applied as the original fertilizer, and the case where urea phosphate phosphorus 48 No. 500 g / 5 m ² and potassium chloride 200 g / 5 m ² are used in combination. Carried out.

In case of applying urea ammonium sulfate 48 and potassium chloride to the original fertilizer, additional fertilization is carried out separately when no additional fertilization is performed and when additional fertilization is performed every month and every 2 months. did. In this additional fertilization, 200 g / 5 m ² of potassium chloride was applied as a solid from one month after sowing.

  For harvesting, the above-ground part of the plant body was collected by mowing every month. The plant height at harvest was 30 cm in November, 50-60 cm in December, 60 cm in January, 70-80 cm in March.

The plants are extracted at regular intervals during the cultivation period, air-dried, adjusted to decompose the plants with a mixed acid of perchloric acid and nitric acid, the residue is filtered, and the resulting solution is used for the above atomic absorption spectrometer, The concentrations of cadmium and zinc in the plant were quantified.
Table 2 shows the concentrations of cadmium and zinc in the plant.

  In “Fertilization method” in Table 2, “No potassium chloride spraying” means that only phosphorous sulfide 48 urea was applied as the basic fertilizer, and “Kali chloride primary fertilizer application” was urea phosphorous sulfide 48 as the primary fertilizer. When potassium chloride is applied and potassium chloride topdressing is not applied, "potassium chloride monthly topdressing" means that urea sulphide No. 48 and potassium chloride are applied as the main fertilizer, and potassium chloride topdressing is 1 When applied every month, "potassium chloride supplemented once every two months" means that when ferrous urea sulfide 48 and potassium chloride are applied as the basic fertilizer, and potassium chloride topdressing is applied every two months To do.

<About the behavior of soil pH and electrical conductivity during the cultivation period>
In order to grasp the effect of fertilizers applied on plants, soil was sampled in conjunction with plant collection during the cultivation period, and its pH and electrical conductivity (EC) were measured.

The soil pH was measured by the glass electrode method after air-drying the soil, adding 25 mL of ionic water to 10 g of soil of 2 mm or less, shaking for 30 minutes, allowing to stand for 30 minutes.
The electrical conductivity was measured after adding 50 mL of ionic water to 10 g of soil and shaking for 1 hour.
The results of soil pH and electrical conductivity are shown in Table 3.

[Comparative Examples 1-8]
Other than changing the plant to be grown to Amri II, the Oat Cultivation Type, Rye Wheat Leister, Rai Wheat Raitaro, Italian Ryegrass Wase Food, Italian Ryegrass Hero, Green Fertilizer Mustard, and Fasceria, Cultivation was carried out in the same manner as in Example 1. Measurement of cadmium and zinc in the harvested plant body was carried out in the same manner as in Example 1.

Moreover, soil pH and electrical conductivity were measured by the same method as Example 1.
Table 4 shows the concentrations of cadmium and zinc in the plant, and Table 5 shows the results of soil pH and electrical conductivity.

  From the results of Example 1 and Comparative Examples 1 to 8, the amount of cadmium absorbed by the cultivated plant varies between crops and varieties, and among the gramineae, the oat wild species (Negusaretaiji) of Example 1 is comparative examples 1 to 1. It was found that the amount of cadmium absorbed was higher than that of 8. In addition, it was found that the amount of zinc absorbed tends to increase as the amount of cadmium absorbed increases.

  In addition, it was confirmed that cadmium and zinc absorption was promoted by the crop when potassium chloride was fertilized during the cultivation period. In particular, it has been clarified that the wild oat species (Negaretaiji) of Example 1 promotes absorption of cadmium by applying potassium chloride. Moreover, the growth disorder by top fertilization did not occur.

  Furthermore, it was also clarified that the amount of cadmium absorbed by the growing season was not significantly different until the heading season.

  Moreover, in Example 1, soil pH was the range of 6-7.5 during the cultivation period. Further, the electrical conductivity was approximately 60 to 200 μS / cm when potassium chloride was not sprayed, whereas it was 60 to 400 μS / cm when potassium chloride was additionally fertilized.

  From the above results, by growing a plant belonging to the wild oat species (Avena trigosa) in soil, absorbing and accumulating heavy metals in the soil, and harvesting this plant, heavy metals such as cadmium and zinc in the soil can be harvested. It was confirmed that it could be recovered and removed.

It is process drawing which shows an example of the zinc smelting method used for the zinc and / or cadmium collection | recovery method which concerns on this invention.

Claims (5)

After planting the plant belonging to the genus Ovena trigosa in the family Gramineae, absorbing heavy metals in the soil,
A method for removing and recovering heavy metals in soil, wherein the plant is harvested and heavy metals in the soil are recovered.   The method for removing and recovering heavy metals in soil according to claim 1, wherein the plant is at least one selected from the group consisting of Avena trigosa Screb., Hey Oats, and New Oats.   The method for removing and collecting heavy metals in soil according to claim 1 or 2, wherein the plant is cultivated in the soil having a pH of 4.5 to 7.5.   The method for removing and collecting heavy metals in soil according to any one of claims 1 to 3, wherein the heavy metals in the soil are zinc, cadmium, or a compound containing these metals. After harvesting the said plant, this plant is supplied in the smelting furnace used for zinc smelting, and zinc and / or cadmium are collect | recovered in the process of this zinc smelting. Of removing and collecting heavy metals in soil.

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