JP3891372B2 - How to clean contaminated soil - Google Patents
How to clean contaminated soil Download PDFInfo
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- JP3891372B2 JP3891372B2 JP01799198A JP1799198A JP3891372B2 JP 3891372 B2 JP3891372 B2 JP 3891372B2 JP 01799198 A JP01799198 A JP 01799198A JP 1799198 A JP1799198 A JP 1799198A JP 3891372 B2 JP3891372 B2 JP 3891372B2
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- JP
- Japan
- Prior art keywords
- contaminated
- soil
- treatment
- acid
- attrition
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Description
【0001】
【発明の属する技術分野】
本発明はカドミウム、鉛などの重金属などで汚染された土壌を洗浄して、汚染物質を除去する汚染土壌の洗浄方法に関するものである。
【0002】
【従来の技術】
市街地再開発に伴う調査で工場跡地などにおける土壌汚染が判明する事例が近年増加しているが、国内で現時点で行われている土壌汚染対策は、汚染成分の不溶化処理や遮水工事、覆土工事などの周辺環境から汚染土壌を遮断する処置方法が一般的である。しかしながらこの方法は汚染物質そのものが現場に残り、処置後においても土地利用に制限がある。
【0003】
そこで最近は高濃度に汚染された土壌は廃棄して、汚染現場の土を入れ替える処置も行われているが、産業廃棄物の最終処分場が近い将来に不足することは明らかなため欧米で実用化されてきている「土壌洗浄法」の導入が検討され始めている。
【0004】
この「土壌洗浄法」とは、汚染物質を除去するために水または適当な溶媒を用いて土壌から汚染成分を物理的、化学的に抽出分離するものであり、汚染土壌を洗浄して汚染成分を高濃度に含有する粒子を除去し、それにより得られる清浄物を汚染現場の埋め戻しに用いることによって、廃棄物となる汚染物を減容化することを目的としている。したがって得られた清浄物量の、供給された汚染物量に対する割合が高いほど効果的な浄化方法となる。
【0005】
このような汚染土壌を洗浄するために従来提案されている方法には、分級による高濃度汚染粒子の分離除去処理(以下分級処理という)やアトリション処理、比重選別、浮遊選鉱、酸溶液やキレート剤溶液などの溶媒による汚染成分の溶脱処理などがある。
【0006】
分級処理法は、汚染元素を吸着する能力が高い微小粒子を分離除去するとともに、汚染されていない粒度範囲の粒子を清浄物として取り出す目的で行われる。しかし土壌の風化が進みこれに伴って生成した二次鉱物が汚染された微粒子を巻き込んで、汚染されていなかった粒子の表面に固着するようになると、分級処理で取り出される清浄物は非常に少なくなるという問題がある。
【0007】
またアトリション処理法は非汚染粒子表面に汚染物質が付着している場合、粒子同士を擦り合わせることによって摩耗研磨する方法であり、分級前に行うのが一般的である。しかし現状のアトリション処理法では、汚染物質が二次鉱物とともに非汚染粒子表面に固着している場合、長時間処理しても汚染物質を除去しきれない。
【0008】
さらに比重選別法も非汚染粒子の表面に汚染物質が固着している場合には対応できない。また固着している汚染微粒子と内側の非汚染粒子が分かれるまで細かく粉砕すれば浮遊選鉱法での対応は可能だが、回収される清浄物が細かくなりすぎてこれを埋め戻して土地再利用をするには用い難い。
【0009】
酸濃度を非常に高くして汚染成分を溶脱する溶脱処理法によれば、二次鉱物ごと汚染物質を溶解させることが可能となるが、これに用いる試薬使用量が莫大になる上、その処理に長時間処理が必要となる。このように試薬使用量が多いとコストや廃水処理の面から実施は困難となり、かつ処理時間が長くなると処理土壌量を確保するためには設備を大型化せざるを得ず、いずれも実施の上から問題となっている。
【0010】
【発明が解決しようとする課題】
本発明は上記の問題点を解決するため、非汚染粒子表面に強固に固着した汚染物質を効率よく分離除去することができる汚染土壌の洗浄方法を提供することを目的とするものである。
【0011】
【課題を解決するための手段】
本発明者らは鋭意研究を重ねた結果、表面に汚染物質が固着している土壌粒子に対して酸を添加するのと同時、または添加後に強いアトリション処理を加えることにより粒子表面に強固に固着した汚染物質を効率よく分離除去することができることを見出し本発明を完成するに至った。
【0012】
したがって上記目的を達成するため本発明は、重金属などにより汚染された土壌を洗浄する方法において、該汚染土壌に酸を添加するのと同時、または添加後に強いアトリション処理を加える汚染土壌の洗浄方法を特徴とするものである。
【0013】
【発明の実施の形態】
本発明は重金属などによる土壌汚染において、高濃度で汚染を含有する微粒子を巻き込みながら、非汚染粒子表面に固着する二次鉱物層を酸と反応させて溶解または脆化しながら強いアトリション処理を行い、通常のアトリション処理や酸溶解処理単独では浄化できなかった土壌粒子を清浄土として回収するものである。
【0014】
すなわち本発明では、硝酸、塩酸、硫酸などの酸の作用によって二次鉱物のうち炭酸塩などの酸と反応し易い鉱物から溶解または変質が進み、二次鉱物層全体としては薄層化および脆化を起こす。ここで強いアトリション処理を加えると、薄層化および脆化した二次鉱物ごと汚染物質を剥ぎ取り、内部の非汚染粒子を得ることができる。したがって二次鉱物層全体を溶解する必要がないため単なる溶解処理と比較して少ない酸投入量および処理時間で、通常のアトリション処理単独では対応できない土壌からも清浄物を得ることができるものである。
【0015】
本発明における強いアトリション処理とは、ドラム型スクラバーや、ドラムウォッシャー、窯業原料の選鉱時に用いられるアトリションマシンなどの装置を用いて回転数30〜100回/分で、5〜60分間行って実施するものであり、これにより強いアトリションを汚染土壌に対してより効率的に加えることができる。しかしドラム型スクラバーやドラムウォッシャーでアトリション処理する場合には、液体を重量比で固液比6:4以上の割合で加えるとアトリション効率が大きく低下するので、該割合未満でアトリション処理をする必要がある。この強いアトリション処理は酸を添加するのと同時に実施することも、あるいは酸添加後放置して酸の作用が進んでから実施することもできる。
【0016】
【実施例】
次に本発明の実施例を、比較例とともに説明する。
硫化カドミウムと硫化鉛で汚染された粒径75〜2000μmの砂に対して、実施例1、比較例1〜3の4通りの処理を行った結果をまとめて表1に示す。
1997年現在での土壌汚染に関する基準としては、環境庁の「重金属等に係る土壌汚染対策指針」があり、そこではCdに対しては9mg/kg、Pbに対しては600mg/kgという含有量参考値が示されている。
【0017】
実施例1
試験対象砂2kgを水480ミリリットル、14N硝酸20ミリリットルとともに容積10リットルのドラム型スクラバーへ投入し、回転数50回/分の酸添加強アトリション処理を15分間行った後、目開き75μmの篩で湿式分級し、粒径75μm以上の粒子を回収した。
【0018】
比較例1
試験対象砂2kgを水500ミリリットルとともに容積10リットルのドラム型スクラバ−へ投入し、回転数50回/分のアトリション処理を1時間行った後、目開き75μmの篩で湿式分級し、粒径75μm以上の粒子を回収した。
【0019】
比較例2
試験対象砂2kgを水20リットル、14N硝酸200ミリリットルとともに撹拌羽根付き水槽中に投入し、羽根回転数700回/分の酸溶解処理を1時間行った後、目開き75μmの篩で湿式分級し、粒径75μm以上の粒子を回収した。
【0020】
比較例3
試験対象砂2kgを水1980ミリリットル、14N硝酸20ミリリットルとともに容積10リットルのドラム型スクラバーへ投入し、回転数50回/分の酸添加アトリション処理を15分間行った後、目開き75μmの篩で湿式分級し、粒径75μm以上の粒子を回収した。
【0021】
【表1】
【0022】
【発明の効果】
以上述べた通り本発明によれば、非汚染粒子表面に固着した汚染物質を分離除去するための酸添加強アトリション処理を組み入れたことにより、従来の単なるアトリション処理や酸溶解処理では浄化できない汚染物質が非汚染粒子表面に強固に固着した土壌から効率よく清浄土を取り出すことができるようになり、また従来の処理方法よりも所要時間が短縮されたり、所要試薬量を節減することができる効果がある。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for cleaning contaminated soil, in which soil contaminated with heavy metals such as cadmium and lead is washed to remove pollutants.
[0002]
[Prior art]
In recent years, there have been an increase in cases where soil contamination is found in factory sites, etc., as a result of surveys related to urban redevelopment. A treatment method that blocks contaminated soil from the surrounding environment is generally used. However, this method leaves the pollutant itself in the field and has limited land use after treatment.
[0003]
Therefore, recently, soil contaminated with a high concentration has been disposed of and replaced with soil at the contaminated site, but it is clear that the final disposal site for industrial waste will be insufficient in the near future. The introduction of the “soil cleaning method” that has become commonplace is beginning to be considered.
[0004]
This “soil cleaning method” is a method in which contaminated components are physically and chemically extracted and separated from the soil using water or an appropriate solvent to remove the pollutants. The purpose is to reduce the volume of pollutants that become waste by removing particles containing a high concentration of and using the resulting clean materials for backfilling the contaminated site. Therefore, the higher the ratio of the obtained amount of clean matter to the amount of supplied contaminants, the more effective purification method.
[0005]
Conventionally proposed methods for washing such contaminated soil include separation / removal treatment (hereinafter referred to as classification treatment) of high-concentration contaminated particles by classification, attrition treatment, specific gravity sorting, flotation, acid solution and chelate. There is a leaching treatment of contaminating components with a solvent such as an agent solution.
[0006]
The classification treatment is performed for the purpose of separating and removing fine particles having a high ability to adsorb contaminating elements and taking out particles in a particle size range that is not contaminated as a clean product. However, when the weathering of the soil progresses and the secondary minerals that accompany it are entrained with contaminated fine particles and stick to the surface of the uncontaminated particles, very little of the clean materials are removed by the classification process. There is a problem of becoming.
[0007]
In addition, the attrition method is a method of abrasion polishing by rubbing particles together when contaminants adhere to the surface of non-contaminated particles, and is generally performed before classification. However, in the current attrition treatment method, when the contaminant is fixed to the surface of the non-contaminated particle together with the secondary mineral, the contaminant cannot be removed even after treatment for a long time.
[0008]
Furthermore, the specific gravity sorting method cannot cope with the case where contaminants adhere to the surface of non-contaminating particles. In addition, it is possible to cope with the flotation method if it is finely pulverized until the adhering contaminated fine particles and the inner non-contaminated particles are separated, but the recovered waste becomes too fine to refill and reuse the land. It is difficult to use.
[0009]
According to the leaching treatment method in which the acid concentration is made extremely high and the contaminated components are leached, it becomes possible to dissolve the pollutants together with the secondary minerals. Long processing is required. In this way, if the amount of reagent used is large, implementation becomes difficult from the viewpoint of cost and wastewater treatment, and if the treatment time is long, the facility must be enlarged to secure the amount of treated soil. It is a problem from above.
[0010]
[Problems to be solved by the invention]
In order to solve the above problems, an object of the present invention is to provide a method for cleaning contaminated soil that can efficiently separate and remove contaminants firmly fixed to the surface of non-contaminated particles.
[0011]
[Means for Solving the Problems]
As a result of intensive research, the inventors of the present invention have made the particle surface firmly by adding a strong attrition treatment at the same time as or after the addition of the acid to the soil particles having the contaminants fixed on the surface. It has been found that the adhered contaminants can be separated and removed efficiently, and the present invention has been completed.
[0012]
Therefore, in order to achieve the above object, the present invention provides a method for cleaning contaminated soil in which a strong attrition treatment is performed simultaneously with or after the addition of acid to the contaminated soil in a method for cleaning soil contaminated with heavy metals. It is characterized by.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The present invention performs a strong attrition treatment while dissolving or embrittlement by reacting a secondary mineral layer adhering to the surface of non-contaminated particles with an acid while entraining fine particles containing contamination at a high concentration in soil contamination with heavy metals and the like. The soil particles that could not be purified by ordinary attrition treatment or acid dissolution treatment alone are recovered as clean soil.
[0014]
That is, in the present invention, dissolution or alteration proceeds from a mineral that easily reacts with an acid such as carbonate among secondary minerals by the action of an acid such as nitric acid, hydrochloric acid, or sulfuric acid, and the secondary mineral layer as a whole becomes thin and brittle. Cause When a strong attrition treatment is applied here, the contaminants can be peeled off together with the thinned and embrittled secondary minerals to obtain non-contaminated particles inside. Therefore, since it is not necessary to dissolve the entire secondary mineral layer, it is possible to obtain a clean product from soil that cannot be handled by ordinary attrition alone, with a small amount of acid input and treatment time compared to simple dissolution treatment. is there.
[0015]
The strong attrition treatment in the present invention is performed for 5 to 60 minutes at a rotation speed of 30 to 100 times / min using an apparatus such as a drum type scrubber, a drum washer, or an attrition machine used for mineral processing of ceramic raw materials. It is what is done, so that strong attrition can be applied more efficiently to contaminated soil. However, when performing attrition with a drum-type scrubber or drum washer, if the liquid is added at a weight ratio of 6: 4 or more, the attrition efficiency is greatly reduced. There is a need to. This strong attrition treatment can be carried out at the same time as the addition of the acid, or can be carried out after the addition of the acid and the action of the acid proceeds.
[0016]
【Example】
Next, examples of the present invention will be described together with comparative examples.
Table 1 summarizes the results of the four treatments of Example 1 and Comparative Examples 1 to 3 performed on sand having a particle size of 75 to 2000 μm contaminated with cadmium sulfide and lead sulfide.
As a standard for soil contamination as of 1997, there is the “Soil Contamination Countermeasure Guidelines for Heavy Metals, etc.” of the Environment Agency, where the content is 9 mg / kg for Cd and 600 mg / kg for Pb. Reference values are shown.
[0017]
Example 1
2 kg of test sand is put into a drum-type scrubber with a capacity of 10 liters together with 480 ml of water and 20 ml of 14N nitric acid, subjected to acid addition strong attrition treatment at a rotation speed of 50 times / min for 15 minutes, and then a sieve having an opening of 75 μm. And wet classification was performed to collect particles having a particle size of 75 μm or more.
[0018]
Comparative Example 1
2 kg of sand to be tested is put into a drum-type scrubber with a capacity of 10 liters together with 500 ml of water, subjected to an attrition treatment at a rotation speed of 50 times / minute for 1 hour, and then wet-classified with a sieve having an opening of 75 μm. Particles of 75 μm or more were collected.
[0019]
Comparative Example 2
2 kg of sand to be tested is put into a water tank with stirring blades together with 20 liters of water and 200 ml of 14N nitric acid, and after 1 hour of acid dissolution treatment with blade rotation speed of 700 times / min, wet classification is performed with a sieve having an opening of 75 μm. Then, particles having a particle diameter of 75 μm or more were collected.
[0020]
Comparative Example 3
2 kg of test sand is put into a drum-type scrubber with a volume of 10 liters together with 1980 ml of water and 20 ml of 14N nitric acid, and after 15 minutes of acid addition attrition treatment at a rotation speed of 50 times / min, a sieve with an opening of 75 μm is used. Wet classification was performed to collect particles having a particle size of 75 μm or more.
[0021]
[Table 1]
[0022]
【The invention's effect】
As described above, according to the present invention, it is impossible to purify by the conventional simple attrition treatment or acid dissolution treatment by incorporating the acid addition strong attrition treatment for separating and removing the contaminants fixed on the surface of the non-contamination particles. Clean soil can be efficiently removed from soil where contaminants are firmly adhered to the surface of non-contaminated particles, and the required time can be shortened and the amount of reagent required can be reduced compared to conventional treatment methods. effective.
Claims (1)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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JP01799198A JP3891372B2 (en) | 1998-01-14 | 1998-01-14 | How to clean contaminated soil |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
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JP01799198A JP3891372B2 (en) | 1998-01-14 | 1998-01-14 | How to clean contaminated soil |
Publications (2)
Publication Number | Publication Date |
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JPH11197643A JPH11197643A (en) | 1999-07-27 |
JP3891372B2 true JP3891372B2 (en) | 2007-03-14 |
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JP01799198A Expired - Fee Related JP3891372B2 (en) | 1998-01-14 | 1998-01-14 | How to clean contaminated soil |
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JP5818095B2 (en) * | 2012-02-28 | 2015-11-18 | 清水建設株式会社 | Cleaning treatment method for cesium contaminated soil |
JP5818096B2 (en) * | 2012-02-28 | 2015-11-18 | 清水建設株式会社 | Cleaning treatment method for cesium contaminated soil |
JP2013248559A (en) * | 2012-05-31 | 2013-12-12 | Shimizu Corp | Method for cleaning heavy metal contaminated soil |
JP2014035333A (en) * | 2012-08-10 | 2014-02-24 | Shimizu Corp | Decontamination treatment method for burned ash |
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