JP4353517B2 - Cleaning agent for organic arsenic compound contaminated soil and purification method - Google Patents

Description

  The present invention relates to the purification of soil contaminated with organic arsenic compounds derived from improperly disposed old chemical weapons, and more specifically, organic arsenic compounds from soil contaminated with organic arsenic compounds. The present invention relates to a cleaning agent and a purification method for contaminated soil, which can reduce the environmental risk due to organic arsenic compounds by extracting and removing with high efficiency, and enables healthy use of land.

In August 2002, it was found that health hazards occurred due to continuous intake of well water contaminated with organic arsenic compounds among residents in Kamisu-cho, Ibaraki Prefecture (Non-Patent Document 1). Diphenylarsinic acid, bisdiphenylarsine oxide, and phenylarsonic acid, which are organic arsenic compounds, were detected from soil and well water. Each of these compounds is a compound in which a phenyl group (C ₆ H ₅ —) is bonded to an arsenic atom (As), and inorganic compounds such as arsenic acid (H ₃ AsO ₄ ) and arsenous acid (H ₃ AsO ₃ ). Arsenic compounds have completely different properties. The structural formulas of typical organic arsenic compounds and inorganic arsenic compounds are described below.

［ここで、（Ｉ）はジフェニルアルシン酸、（II）はビスジフェニルアルシンオキサイド、（III）はフェニルアルソン酸、（IV）はヒ酸、（V）は亜ヒ酸を示す］
有機ヒ素化合物は、親油性を有し、無機ヒ素化合物は親水性を示す。汚染原因となった有機ヒ素化合物はくしゃみ作用や嘔吐作用を催す旧式の化学兵器に由来するものとされている。つまり、第二次世界大戦終結時に不適切に埋立て処分された化学剤が地中で加水分解、酸化などの反応を経て生成したものと考えられている。

[Wherein (I) represents diphenylarsinic acid, (II) represents bisdiphenylarsine oxide, (III) represents phenylarsonic acid, (IV) represents arsenic acid, and (V) represents arsenous acid]
The organic arsenic compound has lipophilicity, and the inorganic arsenic compound exhibits hydrophilicity. The organic arsenic compounds that cause pollution are said to be derived from older chemical weapons that sneeze and vomit. In other words, it is believed that chemical agents that were improperly landfilled at the end of World War II were generated through reactions such as hydrolysis and oxidation in the ground.

  In order to fundamentally solve these problems related to organic arsenic compounds, excavated chemical agents are disposed of appropriately so as not to cause secondary contamination, and soil contaminated with organic arsenic compounds is reliably purified. There is a need to.

  Several methods have been proposed so far for the purification of soil contaminated with arsenic (for example, Patent Documents 1 to 3), all of which are directed to inorganic arsenic compounds. So far, no purification technology has been developed for soil contaminated with compounds.

  For this reason, a heating method has been proposed for the purpose of treating an organic arsenic compound itself derived from a chemical weapon (Non-Patent Document 2). This is an attempt to remove organic arsenic compounds from soil by oxidizing and decomposing them into inorganic arsenic. However, as will be described later, even if the soil contaminated with organic arsenic is simply heated, most of the arsenic remains in the soil, and it is difficult to purify the contaminated soil. That is, in order to solve the problem of soil contamination due to organic arsenic, a technique replacing the heating method is required.

JP-A-11-156338 Japanese Patent Laid-Open No. 2001-225052 Japanese Patent No. 3407039 “Abstracts of 11th Arsenic Symposium” [October 2003] Kazuhiro Ishii, Satoshi Tamoka, Fujio Otsuka; Well water contamination and health effects due to diphenylarsinic acid, etc. Cabinet Office homepage [http://www8.cao.go.jp/ikikagaku/index.html]

  The present invention provides a purification technology that can reduce the environmental risk due to organic arsenic compounds by efficiently extracting and removing organic arsenic compounds from contaminated soil by washing treatment, and enable the sound use of land. With the goal.

  In order to achieve the above object, the present invention firstly analyzed the interaction between an organic arsenic compound and various soils or clay samples, and prepared simulated contaminated soil based on the results. In the simulated contaminated soil, phenylarsonic acid was used as the model organic arsenic compound, and tan forest soil having high adsorptivity with phenylarsonic acid was used as the model soil.

  As a result of repeated trial and error on the effectiveness of the washing treatment with many chemicals using the simulated contaminated soil prepared as described above, unexpectedly, sodium hydroxide, phosphoric acid or its salt, sulfuric acid, hydrochloric acid, tartaric acid or The present invention was completed by finding that an aqueous solution containing at least one of the salt, citric acid or a salt thereof, oxalic acid or a salt thereof has a specific cleaning action on an organic arsenic compound.

That is, the 1st aspect of this invention is the cleaning agent of the organic arsenic compound contamination soil which the phenyl group couple | bonded with the arsenic atom comprised by the aqueous solution containing sodium hydroxide.

A second aspect of the present invention is an arsenic composed of an aqueous solution containing at least one component of phosphoric acid or a salt thereof, sulfuric acid, hydrochloric acid, tartaric acid, citric acid or a salt thereof, or oxalic acid or a salt thereof. It is a cleaning agent for soil contaminated with organic arsenic compounds in which a phenyl group is bonded to an atom .

  According to a third aspect of the present invention, in the first or second aspect, the organic arsenic compound is phenylarsonic acid, diphenylarsinic acid, or bisdiphenylarsine oxide. is there.

According to a fourth aspect of the present invention, there is provided an organic arsenic compound-contaminated soil having a phenyl group bonded to an arsenic atom, wherein the contaminated soil is washed with the cleaning agent according to any one of the first to third aspects. It is a purification method.

According to a fifth aspect of the present invention, there is provided a soil collecting step of collecting soil contaminated with an organic arsenic compound in which a phenyl group is bonded to an arsenic atom, an aqueous solution containing sodium hydroxide in the collected contaminated soil, phosphoric acid Or an aqueous solution containing a salt thereof, an aqueous solution containing sulfuric acid, an aqueous solution containing hydrochloric acid, an aqueous solution containing tartaric acid or a salt thereof, an aqueous solution containing citric acid or a salt thereof, or an aqueous solution containing oxalic acid or a salt thereof, An extraction process for transferring an organic arsenic compound in soil into an aqueous solution by mixing any of the above, and a solid-liquid separation process for separating the aqueous solution containing the organic arsenic compound from the soil, This is a method for purifying soil contaminated with an organic arsenic compound in which a phenyl group is bonded to an arsenic atom .

  According to the present invention, an organic arsenic compound can be extracted and removed easily and with high efficiency from a soil contaminated with an organic arsenic compound in a short period of time.

<Cleaning agent>
In a preferred embodiment, the cleaning agent of the present invention is an aqueous solution containing sodium hydroxide, an aqueous solution containing phosphoric acid or a salt thereof, an aqueous solution containing sulfuric acid, an aqueous solution containing hydrochloric acid, or an aqueous solution containing tartaric acid or a salt thereof. Or an aqueous solution containing citric acid or a salt thereof, or an aqueous solution containing oxalic acid or a salt thereof.

  The treatment target of the present invention is not particularly limited as long as it is soil contaminated with an organic arsenic compound. As will be described later, the adsorptivity of the organic arsenic compound varies greatly depending on the type of soil, but the cleaning agent of the present invention is effective for any type of soil. Of course, the active ingredient of the cleaning liquid can also be selected according to the type of contaminated soil. In addition, since the physical or chemical properties of the soil are thought to affect the purification efficiency, pretreatment operations such as crushing, classification, dehydration, and pH adjustment are performed as necessary for the purpose of enhancing the cleaning effect. Can be applied.

  Examples of organic arsenic compounds that are pollutants include diphenylarsinic acid, bisdiphenylarsine oxide, and phenylarsonic acid. All of these substances are lipophilic and remain in the soil for a long time in the natural state.

  The active ingredient of the cleaning agent of the present invention is sodium hydroxide, phosphoric acid or a salt thereof, sulfuric acid, hydrochloric acid, tartaric acid or a salt thereof, citric acid or a salt thereof, or oxalic acid or a salt thereof. Examples of the salt include sodium salt and potassium salt, and examples of the phosphoric acid salt include sodium phosphate, sodium hydrogen phosphate (sodium dihydrogen phosphate, disodium hydrogen phosphate), potassium phosphate, phosphorus Potassium hydrogen hydrogen (potassium dihydrogen phosphate, dipotassium hydrogen phosphate), tartaric acid salt, sodium tartrate, potassium tartrate, citric acid salt, sodium citrate, potassium citrate, etc., as oxalic acid salt Can include sodium oxalate, potassium oxalate, and the like.

  In the present invention, not only an aqueous solution containing the above active ingredient alone, but also an aqueous solution containing, for example, a combination of two or more acids can be prepared as a cleaning agent.

  The type and concentration of the active ingredient in the cleaning agent can be appropriately selected according to the type of soil and its state (water content, pH, particle size, etc.), the type of organic arsenic compound, the concentration of contamination, and the like. In particular, the concentration of the active ingredient in the aqueous solution is not limited, and it is generally considered that the higher the concentration, the higher the arsenic removal action. Is preferred. For example, the concentration of sodium hydroxide in the aqueous solution containing sodium hydroxide is preferably 1N or less, and more preferably about 0.05N to 0.5N. Further, the concentration of phosphoric acid or a salt thereof in an aqueous solution containing phosphoric acid or a salt thereof is preferably 10% or less, and more preferably about 0.5 to 5%. The concentration of sulfuric acid in the aqueous solution containing sulfuric acid is preferably 10% or less, and more preferably about 1 to 5%. The concentration of hydrochloric acid in the aqueous solution containing hydrochloric acid is preferably 10% or less, and more preferably about 1 to 5%. The concentration of tartaric acid or a salt thereof in tartaric acid or a salt thereof is preferably 20% or less, and more preferably about 5 to 15%. The concentration of citric acid or a salt thereof in an aqueous solution containing citric acid or a salt thereof is preferably 20% or less, and more preferably about 5 to 15%. The concentration of oxalic acid or a salt thereof in an aqueous solution containing oxalic acid or a salt thereof is preferably 10% or less, and more preferably about 1 to 5%. As exemplified above, in the present invention, since purification can be performed with a relatively low concentration alkali or aqueous acid solution, the amount of chemicals used and the burden of wastewater treatment are small, and the economy is high.

  Further, in the aqueous solution as a cleaning agent, for example, a surfactant or the like can be added as long as the cleaning action on the organic arsenic compound is not impaired. By the addition of the surfactant, the cleaning agent may penetrate into the dense soil layer, and the elution of the organic arsenic compound in the soil may be promoted.

<Purification method of organic arsenic compound contaminated soil>
The purification method according to the present invention is carried out by treating organic arsenic compound-contaminated soil with the cleaning agent. As an example of treatment with a cleaning agent, for example, soil contaminated with an organic arsenic compound is collected (soil sampling step), and the organic arsenic compound in the soil is mixed by mixing the cleaning agent with the collected contaminated soil. It is carried out by transferring into an aqueous solution (extraction step) and then separating the aqueous solution containing the organic arsenic compound from the soil (solid-liquid separation step).

  More specifically, the organic arsenic compound-contaminated soil is sampled from the ground by means such as excavation, carried into a predetermined cleaning device, an appropriate amount of aqueous solution is added, and after mixing and stirring with a stirrer or the like, the aqueous solution And solid-liquid separation by a method such as centrifugation, filtration, or stationary separation. When extracting the organic arsenic compound, elution of the organic arsenic compound in the soil granule can be promoted by mixing and stirring, and the organic arsenic compound can be efficiently transferred into the aqueous solution. In solid-liquid separation, an aggregating agent such as a cationic polymer may be added as necessary to coagulate and settle the soil components.

  Further, as another embodiment of the purification method, the column can be filled with contaminated soil and the cleaning solution can be passed from the top or bottom of the column. As another aspect, it is also possible to carry out by a method of taking contaminated soil in a container, adding a cleaning liquid thereto and immersing it for a predetermined time, and then discharging the cleaning liquid from the bottom of the container.

  In the above process, there are cases where the extraction efficiency can be improved by using an aqueous solution preheated to a temperature from room temperature to about 90 ° C. or by performing the extraction operation while heating. In addition, the amount of the aqueous solution used as a cleaning agent is not particularly limited and does not prevent excessive use with respect to the volume of contaminated soil, but considering the wastewater treatment after extraction of the organic arsenic compound, the volume ratio to the contaminated soil is It is preferable to apply in the range of about 1/2 to 10 times.

  By treating the soil as described above, the cleaning liquid containing the extracted arsenic is recovered. This recovered cleaning liquid can be treated as waste water, but can also be recycled as a cleaning agent until the arsenic concentration and the concentration of dissolved soil components reach predetermined values.

  In the purification treatment of contaminated soil, not only a single cleaning agent but also two or more cleaning agents with different active ingredients and concentrations (for example, phosphoric acid and hydrochloric acid, 1% phosphoric acid and 3% phosphoric acid, etc.) The multi-step cleaning process may be performed sequentially using

<Action>
As understood from the difference in the chemical structural formula, the organic arsenic compound is significantly different in chemical properties from the inorganic arsenic compound that has conventionally caused soil contamination. Since organic arsenic compounds are lipophilic, it was predicted that they cannot be sufficiently extracted with an aqueous solution of acid or alkali. For this reason, although the present inventors tried extraction using alcohols, such as methanol and ethanol, initially, the favorable result was not obtained as shown in a postscript comparative example.

  Organic arsenic compounds in soil are highly compatible solvents because arsenic atoms are chemically adsorbed to iron atoms in iron hydroxide contained in the soil or aluminum atoms in aluminum hydroxide via oxygen atoms. However, it is not considered to elute easily. Moreover, although the heating method was also tried, sufficient removal effect was not acquired even more than volatilization and decomposition temperature, as shown in the comparative example mentioned later.

  However, as a result of trial and error, contrary to the above prediction, by using an aqueous solution of a specific alkali or acid, it is experimentally found that a remarkable extraction and cleaning effect can be obtained compared with cleaning with alcohols or heat treatment. confirmed. Extraction with a specific acid aqueous solution or alkaline aqueous solution is effective for organic arsenic compounds in soil (in other words, a specific acid or alkaline aqueous solution has an action of removing organic arsenic compounds in soil ) Is a finding first discovered by the present inventors.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not restrict | limited by these. In Examples and the like, preparation of simulated contaminated soil, heat treatment experiment, and washing experiment were performed according to the following procedure.

<Preparation of simulated contaminated soil>
2 liters of an aqueous phenylarsonic acid solution having an initial concentration of 462 ppm (as arsenic) and an initial pH of 2.93 was prepared in a 3 liter polyethylene bottle. About 1 kg of tan forest soil (collected in Tsukuba City, Ibaraki Prefecture) was added thereto, and the mixture was shaken in a horizontal direction (amplitude 10 cm) for 5 days with a shaker at room temperature. The supernatant was removed and washed with about 1 liter of deionized water. This operation was repeated three times.

  The obtained slurry was filtered using qualitative filter paper, and the filter cake was air-dried, further dried under reduced pressure, and stored in a sealed polyethylene bottle. The arsenic content of this pseudo-contaminated soil was 897 mg / kg.

<Heat treatment experiment procedure>
4 g of the simulated contaminated soil was taken in a magnetic boat (width 17 mm × length 100 mm × depth 12 mm) and inserted into a quartz tube (inner diameter 18 mm × length 1000 mm) installed in a cylindrical electric furnace. Air or nitrogen gas was passed as a carrier gas at a flow rate of 250 ml / min, and the electric furnace was energized to maintain the sample temperature at 200 ° C., 400 ° C., and 600 ° C. for 30 minutes.

  The carrier gas emerging from the quartz tube was passed through two gas cleaning bottles to collect arsenic in the gas phase. The first gas washing bottle was charged with 200 ml of methanol, and the second with 1N sodium hydroxide solution.

  The arsenic concentration in the obtained methanol and sodium hydroxide solution was measured by graphite furnace atomic absorption spectrophotometry. In addition, after heat treatment, the soil sample was decomposed with nitric acid and hydrogen peroxide according to the method of EPA 3050B (sample decomposition method defined by the US Environmental Protection Agency: method 3050B), and then measured for arsenic concentration by ICP emission spectroscopy The amount of arsenic remaining in the soil was determined.

<Cleaning experiment procedure>
A 35 ml polycarbonate centrifugal sedimentation tube was charged with 1 g of simulated contaminated soil and 25 ml of an aqueous cleaning solution, and shaken in a constant temperature bath maintained at 20 ° C. in a horizontal direction (amplitude 10 cm) for a predetermined time. Subsequently, it centrifuged at 9,000 rpm for 20 minutes using the high-speed centrifuge with a refrigerator, and the isolate | separated supernatant liquid was filtered with the membrane filter with the hole diameter of 0.2 micrometer. For the obtained filtrate, the arsenic concentration was measured by ICP emission spectrometry or graphite furnace atomic absorption spectrometry, and the concentrations of aluminum, iron, magnesium, calcium, and silica were measured by ICP emission analysis.

Reference example 1
Analysis of interactions between organic arsenic compounds and soil:
As soil samples, pseudo-grayed yellow-brown forest soil, yellow-brown forest soil (1), yellow-brown forest soil (2), sulfuric acid-grade gray soil, Kanuma soil, Kuroboku soil, Kuroboku soil soil, wet humus type Podosol soil, red yellow soil (1), red yellow soil (2) and volcanic ash, and clay samples such as Kaolinite # 1101, Dickite # 1301, Pyrophyllite # 2101, montmorillonite ( A total of 19 samples of Montmorillonite # 3101, Montmorillonite # 3102, Sericite # 5101, Cleavage Sericite # 5102, and shale clay were subjected to phenylarsonic acid adsorption tests.

  About 0.25 g of each sample was placed in a 35 ml polycarbonate centrifugal sedimentation tube, and 25 ml of an aqueous phenylarsonic acid solution having an initial concentration of 14.1 ppm (as arsenic) and an initial pH of 4.00 was added. The centrifugal precipitation tube was shaken in a constant temperature bath maintained at 20 ° C. in a horizontal direction (amplitude 10 cm) with a shaker for a predetermined time. Subsequently, it centrifuged at 9,000 rpm for 20 minutes using the high-speed centrifuge with a refrigerator, and the isolate | separated supernatant liquid was filtered with the 0.45 micrometer pore size membrane filter. About the obtained filtrate, arsenic concentration was measured by the graphite furnace atomic absorption spectrophotometry. The result is shown in FIG.

  From FIG. 1, phenylarsonic acid was hardly adsorbed on clay samples except kaolinite and shale clay. In soil samples, the adsorption rate of phenylarsonic acid changed greatly depending on the type of soil. Among the soil samples, pseudo-grayed yellow-brown forest soil, yellow-brown forest soil (1), and sulfate-based clay soil showed high adsorption rates. From this test, it was shown that the adsorptivity of organic arsenic compounds to soil varies greatly depending on the types of soil components.

Comparative Example 1
Purification test by heating method:
According to the heat treatment experiment procedure, the simulated contaminated soil was heated at 200 ° C., 400 ° C. or 600 ° C. in an air or nitrogen gas atmosphere. In either case, the arsenic concentration in the methanol and sodium hydroxide solution in the gas cleaning bottle was very small, and it was confirmed that the arsenic was hardly volatilized by the heat treatment.

  On the other hand, as shown in FIG. 2, it was recognized that 80 to 118% of arsenic remained in the soil after the heat treatment on the basis of before the heat treatment. This indicates that it is difficult to remove soil contaminated with phenylarsonic acid from the soil simply by heating.

  The melting point of phenylarsonic acid is 158 to 162 ° C., and melting occurs with decomposition. Therefore, it was predicted that decomposition and vaporization would be complete at a heating temperature of 200 ° C. or higher. However, as shown in the experimental results, arsenic could not be removed even when heated to 200 ° C. or higher. As a reason why arsenic was not volatilized, as described later, it is presumed that phenylarsonic acid is chemically strongly captured in the soil component. The reason why arsenic in the soil did not evaporate even at 400 ° C. or higher is considered to be that phenylarsonic acid is only oxidized and decomposed into diarsenic trioxide and remains in the soil.

Examples 1-11 and Comparative Examples 2-14
Cleaning method:
According to the washing experiment procedure, the simulated contaminated soil was treated with the detergent shown in Table 1.

得られた結果を図３に示す。土壌中のフェニルアルソン酸は水やアルコール類ではほとんど溶出してこなかったが、実施例１〜１１の特定の酸またはアルカリ水溶液（本発明洗浄剤）では顕著な溶出が確認された。特に、０.１Ｎ水酸化ナトリウムや、３.４％リン酸、１.１％リン酸、２重量％リン酸二水素カリウム、３.８％硫酸、１.３％硫酸などの鉱酸及びその塩で非常に高いヒ素除去率が得られた。また、１０重量％酒石酸、１０重量％クエン酸、２重量％シュウ酸ナトリウムなどの有機酸及びその塩でも５０％以上の高いヒ素除去率が得られた。

The obtained results are shown in FIG. Although phenylarsonic acid in the soil hardly eluted in water or alcohols, remarkable elution was confirmed in the specific acid or alkaline aqueous solution (the cleaning agent of the present invention) of Examples 1-11. In particular, 0.1N sodium hydroxide, 3.4% phosphoric acid, 1.1% phosphoric acid, 2% by weight potassium dihydrogen phosphate, 3.8% sulfuric acid, 1.3% sulfuric acid and other mineral acids and their A very high arsenic removal rate was obtained with the salt. Further, an organic acid such as 10% by weight tartaric acid, 10% by weight citric acid and 2% by weight sodium oxalate and a salt thereof showed a high arsenic removal rate of 50% or more.

  Although phenylarsonic acid is soluble to some extent in water, methanol, ethanol, and isopropyl alcohol, the phenylarsonic acid in the mock-contaminated soil was hardly eluted even when washed with these solvents. This is presumably because the arsenic atom of phenylarsonic acid is in a state of being chemisorbed and trapped on the iron atom in the iron hydroxide in the soil or the aluminum atom in the aluminum hydroxide via the oxygen atom.

  In addition, although the above experiment was implemented using phenylarsonic acid, since the phenylarsonic acid and diphenylarsinic acid are highly similar, the cleaning agent of the present invention is effective for the purification of soil contaminated with diphenylarsinic acid. Is self-evident, and the removal effect on other organic arsenic compounds such as bisdiphenylarsine oxide is also in a range that can be inferred.

  The present invention has been described above with reference to various embodiments. However, the present invention is not limited to the above embodiments, and can be applied to other embodiments within the scope of the invention described in the claims. It is.

  The present invention can be used for purification and regeneration of soil contaminated with organic arsenic compounds.

The graph drawing which shows the adsorption | suction characteristic of phenylarsonic acid by soil kind. The graph drawing which shows the arsenic residual amount in the heat-processed simulation contaminated soil. The graph which shows the removal rate of the organic arsenic compound from the simulation contaminated soil by various cleaning agents.

Claims (5)

A cleaning agent for soil contaminated with organic arsenic compounds in which phenyl groups are bonded to arsenic atoms composed of an aqueous solution containing sodium hydroxide. Organic arsenic having a phenyl group bonded to an arsenic atom composed of an aqueous solution containing at least one component of phosphoric acid or a salt thereof, sulfuric acid, hydrochloric acid, tartaric acid, citric acid or a salt thereof, or oxalic acid or a salt thereof Cleaning agent for compound contaminated soil.   3. The organic arsenic compound-contaminated soil cleaning agent according to claim 1, wherein the organic arsenic compound is phenylarsonic acid, diphenylarsinic acid or bisdiphenylarsine oxide. A method for purifying soil contaminated with an organic arsenic compound in which a phenyl group is bonded to an arsenic atom , wherein the contaminated soil is washed with the cleaning agent according to any one of claims 1 to 3. A soil collection step of collecting soil contaminated with an organic arsenic compound in which a phenyl group is bonded to an arsenic atom ;
The collected contaminated soil is mixed with an aqueous solution containing sodium hydroxide, an aqueous solution containing phosphoric acid or its salt, an aqueous solution containing sulfuric acid, an aqueous solution containing hydrochloric acid, an aqueous solution containing tartaric acid or its salt, citric acid or its An extraction step of transferring an organic arsenic compound in soil into the aqueous solution by mixing either an aqueous solution containing a salt or an aqueous solution containing oxalic acid or a salt thereof;
A solid-liquid separation step of separating the aqueous solution containing the organic arsenic compound and the soil;
A method for purifying soil contaminated with an organic arsenic compound in which a phenyl group is bonded to an arsenic atom .

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