JP6132282B2 - Decontamination method for contaminated soil or contaminated incineration ash - Google Patents
Decontamination method for contaminated soil or contaminated incineration ash Download PDFInfo
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Description
本発明は、汚染された土壌又は焼却灰の除染方法、特に、１３７Ｃｓや１３４Ｃｓ等の放射性物質で汚染された土壌又は焼却灰の除染を効率的に、且つ効果的に行うために、機械的衝撃及び酸化可溶性促進を利用した汚染土壌又は汚染焼却灰の除染方法に関する。 The present invention is a method for decontaminating contaminated soil or incinerated ash, in particular, for efficiently and effectively decontaminating soil or incinerated ash contaminated with radioactive substances such as 137 Cs and 134 Cs. Further, the present invention relates to a decontamination method for contaminated soil or contaminated incineration ash using mechanical impact and oxidative solubility promotion.
原子力発電関連施設等から何らかの原因でセシウム等の放射性物質が大量に外部へ漏れたり飛散したりして土壌表層部が汚染された場合、放射性物質の直接接触や経口摂取等による人体への直接的な影響が懸念されている。特に、放射性物質からの放射線量が多い場合は大きな被害を引き起こしやすい。また、土壌表層部において農作物が栽培されていたり、ゴミ等が放置されている場合は、農作物やゴミへの汚染が発生する。さらに、森林土壌などでは土壌表層部を覆っている落ち葉や草木等への汚染も考慮する必要がある。 If the surface layer of the soil is contaminated due to a large amount of radioactive material such as cesium leaking outside or scattered from nuclear power generation related facilities, etc., direct contact to the human body due to direct contact or ingestion of radioactive material There are concerns about the impact. In particular, if the radiation dose from radioactive material is large, it is likely to cause a great damage. In addition, when crops are cultivated in the soil surface layer or when garbage is left unattended, contamination of the crops and garbage occurs. Furthermore, in forest soils, it is necessary to consider the contamination of fallen leaves and vegetation that cover the soil surface.
このような土壌表層部の汚染に対する除染方法としては、従来から（i）大型機械を用いて表面を削る方法、（ii）高圧洗浄機を用いて水洗する方法、（iii）高分子ゲル又はゼオライトやベントナイト等の無機物によって、汚染物質を付着又は吸着させて除染する方法、（ｉｖ）汚染された土壌をアスファルトや非汚染の土壌や物質で被覆する客土法、（ｖ）植物を利用して汚染物質を除去する技術等が知られている。例えば、特許文献１には、前記の（ｉ）の方法として、土壌表層部を固定することによって、該表層部をその下層の土壌からはぎ取るための方法が提案されている。前記の特許文献１に記載の発明は、放射性物質による汚染領域が土壌深さ数ｃｍ程度の表層部のみに限定されるという点に着目してなされたものである。 Conventional decontamination methods for soil surface layer contamination include (i) a method of scraping the surface using a large machine, (ii) a method of washing with a high-pressure washer, (iii) a polymer gel or Decontamination by adhering or adsorbing pollutants with inorganic substances such as zeolite and bentonite, (iv) Custom soil method to coat contaminated soil with asphalt or non-contaminated soil and substances, (v) Utilizing plants A technique for removing contaminants is known. For example, Patent Document 1 proposes, as the method (i) described above, a method for removing the surface layer portion from the underlying soil by fixing the surface layer portion of the soil. The invention described in Patent Document 1 is made by paying attention to the fact that the contaminated area due to the radioactive substance is limited only to the surface layer portion having a soil depth of about several centimeters.
また、特許文献２には、汚染土壌を汚染サイト（地域）から採取、輸送してから、その汚染土壌そのものの除染を湿式で行う方法が開示されている。前記の特許文献２に記載の発明は、アクチニドもしくはその放射性崩壊生成物もしくは核分裂生成物で汚染された土壌を、非毒性生成物に自然に分解可能な成分を含有する水溶液からなる液体媒体と接触させて処理することによって、土壌をより安全な状態にする方法である。
前記の特許文献１に記載の発明は、放射性物質で汚染された土壌表層部を剥ぎ取るための方法に関するものであり、土壌表層部の除去後の除染方法については記載や示唆が何等されておらず、除染を行った後の土壌の再生や再利用については認識が全くされていなかった。また、除染方法として例示した前記の（iｖ）客土法も汚染土壌のそのものの除染方法に関するものでなく、汚染土壌が存在する地域の処理を広範囲に行うことが困難であり、その地域の再利用や再開発を行うには環境への負荷や安全性を含めて多くの問題が残されている。 The invention described in Patent Document 1 relates to a method for stripping a soil surface layer contaminated with a radioactive substance, and there is no description or suggestion about a decontamination method after the removal of the soil surface layer portion. There was no recognition of soil regeneration and reuse after decontamination. In addition, the above (iv) land-of-soil method exemplified as the decontamination method is not related to the decontamination method of the contaminated soil itself, and it is difficult to treat the area where the contaminated soil exists widely. Many problems remain, including environmental impact and safety, in the reuse and redevelopment.
さらに、前記の（ｉｉ）、（ｉｉｉ）及び（ｖ）の方法は、除染方法として簡便で効率的であるものの、放射性物質の吸着能の点から除染効果が十分でなく、確実な除染を行う方法としてはさらに改良が必要である。 Further, although the above methods (ii), (iii) and (v) are simple and efficient as a decontamination method, the decontamination effect is not sufficient from the viewpoint of the adsorption ability of radioactive materials, and reliable decontamination. Further improvement is required as a method of dyeing.
一方、前記の特許文献２には汚染土壌そのものの除染方法が開示されているが、非毒性生成物に自然に分解可能な成分を含有する水溶液は少なくとも３成分を有する必要があり、除染の効果を十分に発揮するためには、それらの成分の種類と配合量の最適化のための調整が煩雑な作業となる。また、除染の対象物とするセシウム１３７（１３７Ｃｓ）又はセシウム１３4（１３４Ｃｓ）の場合でも、短時間処理で十分な除染効果が得られるか否かが不明である。
On the other hand, although
さらに、放射性物質で汚染された焼却灰についても、単に汚染焼却灰として隔離して保管又は貯蔵のために長期間放置する場合、処理量が膨大となるにつれて保管、貯蔵場所の確保が大きな問題となる。そのため、汚染された焼却灰を長期間に亘って保管又は貯蔵する代わりに、早期に埋立や他の用途へ使用できることが必要であり、効率的で、且つ確実な焼却灰の除染方法が強く望まれている。 In addition, incineration ash contaminated with radioactive substances is also a major problem when it is isolated as contaminated incineration ash and left for storage or storage for a long period of time. Become. Therefore, instead of storing or storing the contaminated incineration ash for a long period of time, it is necessary to be able to use it for landfill and other uses at an early stage, and an efficient and reliable method for decontamination of incineration ash is strong. It is desired.
本発明は、係る問題を解決するためになされたものであり、１３７Ｃｓや１３４Ｃｓ等の放射性物質で汚染された土壌又は焼却灰を回収又は捕集した後に、機械的衝撃及び酸化可溶性促進を利用することによって、除染を効率的に、且つ効果的に行うだけでなく、除染後の土壌や焼却灰の再生及び再利用を促進することができる汚染土壌又は汚染焼却灰の除染方法を提供することを目的とする。 The present invention has been made to solve such a problem. After collecting or collecting soil or incinerated ash contaminated with radioactive substances such as 137 Cs and 134 Cs, mechanical shock and oxidation solubility promotion are achieved. Decontamination method of contaminated soil or contaminated incineration ash that not only efficiently and effectively performs decontamination, but also promotes regeneration and reuse of soil and incinerated ash after decontamination The purpose is to provide.
本発明者は、１３７Ｃｓや１３４Ｃｓ等の放射性物質が、汚染土壌中又は汚染焼却灰中で数１０μｍ程度の顆粒状として存在するために水洗等による除染効果を低下させるという新たな知見に基づいて、水洗等による除染方法を行う前に、機械的衝撃を利用して汚染土壌又は汚染焼却灰をより小さな粒子に粉砕して表面積を増やすだけでなく、さらに、汚染土壌中又は汚染焼却灰中に存在する放射性物質の酸化を促進して水洗等による除染処理の効率を高めることによって、上記の課題を解決できることを見出して本発明に到った。 The present inventor has a new finding that radioactive substances such as 137 Cs and 134 Cs are present in the contaminated soil or contaminated incinerated ash as granules of about several tens of μm, so that the decontamination effect by washing with water is reduced. Based on this, before conducting decontamination methods such as washing with water, the mechanical impact is used to not only increase the surface area by crushing the contaminated soil or contaminated incineration ash into smaller particles, but also in the contaminated soil or incineration. The present inventors have found that the above-mentioned problems can be solved by promoting the oxidation of radioactive substances present in the ash to increase the efficiency of the decontamination treatment by washing with water or the like.
すなわち、本発明の構成は以下の通りである。
［１］本発明は、放射性物物質で汚染された土壌又は焼却灰の除染方法であって、前記放射性物物質で汚染された土壌又は焼却灰を回収又は捕集する工程と、該回収又は捕集する工程後の土壌又は焼却灰を室温又は加温下で機械的に粉砕後の平均粒径が１ｍｍ以下となるまで粉砕する粉砕工程と、該粉砕工程後の土壌又は焼却灰を水洗する水洗工程と、該水洗工程後の土壌又は焼却灰から前記放射性物質を含有する水を分離して回収する分離回収工程とを有することを特徴とする汚染土壌又は汚染焼却灰の除染方法を提供する。
［２］本発明は、前記粉砕工程と水洗工程との間に、前記粉砕工程で粉砕された後の土壌又は焼却灰から粗粒子を選別する選別工程を有することを特徴とする前記［１］に記載の汚染土壌又は汚染焼却灰の除染方法を提供する。
［３］本発明は、前記選別工程において、前記選別される粗粒子は最小粒径が１ｍｍを超えるものであることを特徴とする前記［２］に記載の汚染土壌又は汚染焼却灰の除染方法を提供する。
［４］本発明は、前記［１］〜［３］の何れかに記載の除染方法において、前記放射性物質を含有する水を分離して回収された後に残る土壌又は焼却灰は、放射線線量の検査を行い、前記放射線線量が所定の値以下であれば回収前又は捕集前の元の場所に戻し、前記放射線量が所定の値を超えるときには、少なくとも前記の水洗工程及び分離回収工程を前記放射線線量が所定の値以下になるまで繰り返すことを特徴とする汚染土壌又は汚染焼却灰の除染方法を提供する。
［５］本発明は、前記粉砕工程が、酸化剤の存在下で行われることを特徴とする前記［１］〜［４］の何れかに記載の汚染土壌又は汚染焼却灰の除染方法を提供する。
［６］本発明は、前記の酸化剤が、オゾン、過酸化水素、酸素、塩素酸、過塩素酸及び過マンガン酸カリウムからなる群の少なくとも１つであることを特徴とする前記［５］に記載の汚染土壌又は汚染焼却灰の除染方法を提供する。
［７］本発明は、前記放射性物質を含有する水を分離して回収する分離回収工程が、濾過法、デカンテーション法及び遠心分離法からなる群の少なくとも１つの方法によって行われることを特徴とする前記［１］〜［６］の何れかに記載の汚染土壌又は汚染焼却灰の除染方法を提供する。
［８］本発明は、前記分離回収工程が、前記水洗工程で水洗された土壌又は焼却灰の粒子の中で最小粒径１００μｍを超える粒子を篩を用いて取り除いた後に、前記の濾過法、デカンテーション法及び遠心分離法からなる群の少なくとも１つの方法によって行われることを特徴とする前記［７］に記載の汚染土壌又は汚染焼却灰の除染方法を提供する。
［９］本発明は、前記水洗工程が、前記粉砕工程後の土壌又は焼却灰を水中で混合又は撹拌して行われることを特徴とする前記［１］〜［８］の何れかに記載の汚染土壌又は汚染焼却灰の除染方法を提供する。
［１０］本発明は、前記の粉砕工程が、ボールミルを用いて回転撹拌によって行われることを特徴とする前記［１］〜［９］の何れかに記載の汚染土壌又は汚染焼却灰の除染方法を提供する。
[発明の効果]
That is, the configuration of the present invention is as follows.
[1] The present invention is a method for decontaminating soil or incinerated ash contaminated with a radioactive substance, the step of collecting or collecting the soil or incinerated ash contaminated with the radioactive substance, A pulverization step of mechanically pulverizing the soil or incinerated ash after the collecting step at room temperature or under heating, and washing the soil or incinerated ash after the pulverizing step with water until the average particle size becomes 1 mm or less. Provided is a decontamination method for contaminated soil or contaminated incineration ash, comprising a water washing step and a separation and recovery step for separating and recovering water containing the radioactive substance from the soil or incinerated ash after the water washing step To do.
[ 2 ] The present invention, [1] , characterized by having a sorting step for sorting coarse particles from the soil or incinerated ash pulverized in the pulverization step between the pulverization step and the water washing step . A decontamination method for contaminated soil or contaminated incineration ash as described in 1.
[ 3 ] The decontamination of contaminated soil or contaminated incineration ash according to [ 2 ], wherein the coarse particles to be sorted have a minimum particle size exceeding 1 mm in the sorting step. Provide a method.
[ 4 ] The present invention provides the decontamination method according to any one of [1] to [ 3 ], wherein the soil or incinerated ash remaining after the water containing the radioactive substance is separated and recovered is a radiation dose. If the radiation dose is less than or equal to a predetermined value, it is returned to the original location before collection or before collection, and when the radiation dose exceeds a predetermined value, at least the water washing step and the separation and recovery step are performed. Provided is a decontamination method for contaminated soil or contaminated incineration ash, which is repeated until the radiation dose becomes a predetermined value or less.
[ 5 ] The present invention provides the decontamination method for contaminated soil or contaminated incineration ash according to any one of [1] to [ 4 ], wherein the pulverization step is performed in the presence of an oxidizing agent. To provide .
[6] The present invention, the oxidizing agent is ozone, hydrogen peroxide, oxygen, chlorate, above, wherein the at least one of the group consisting of potassium perchlorate and potassium permanganate [5] A decontamination method for contaminated soil or contaminated incineration ash as described in 1.
[ 7 ] The present invention is characterized in that the separation and recovery step of separating and recovering the water containing the radioactive substance is performed by at least one method of the group consisting of a filtration method, a decantation method and a centrifugation method. Provided is a method for decontamination of contaminated soil or contaminated incinerated ash according to any one of [1] to [ 6 ].
[ 8 ] The present invention provides the filtration method described above, after the separation and recovery step uses a sieve to remove particles having a minimum particle size of 100 μm from the soil or incinerated ash particles washed in the water washing step, The decontamination method for contaminated soil or contaminated incineration ash according to [ 7 ] above, wherein the method is performed by at least one method of the group consisting of a decantation method and a centrifugal separation method.
[ 9 ] The present invention according to any one of [1] to [ 8 ], wherein the water washing step is performed by mixing or stirring the soil or incinerated ash after the crushing step in water. Provide a decontamination method for contaminated soil or contaminated incineration ash.
[ 10 ] The present invention provides the decontamination of contaminated soil or contaminated incinerated ash according to any one of [1] to [ 9 ], wherein the pulverization step is performed by rotary stirring using a ball mill. Provide a method.
[Effect of the invention]
本発明によれば、セシウム等の放射性物質で汚染された土壌又は焼却灰を初期の大きさよりも小さく粉砕して表面積を増やすことによって、前記放射性物質が酸化されやすい環境が創出され、水洗等の簡便な方法を使って効率的で、且つ確実な除染を行うことができる。さらに、粉砕工程を酸化剤の存在下で行うことによって放射性物質の酸化が促進されるため、除染効果の一層の向上が図れる。 According to the present invention, by crushing soil contaminated with radioactive substances such as cesium or incinerated ash smaller than the initial size to increase the surface area, an environment in which the radioactive substances are easily oxidized is created, such as washing with water. Efficient and reliable decontamination can be performed using a simple method. Furthermore, since the oxidation of the radioactive substance is promoted by performing the pulverization step in the presence of an oxidizing agent, the decontamination effect can be further improved.
また、本発明によれば、放射性物質で汚染された土壌又は焼却灰の除染が短時間で十分に行えるため、環境への悪影響を低減し、安全性を高めることができる。それによって、汚染土壌又は汚染焼却灰の再生及び再利用を促進できる。 In addition, according to the present invention, since soil or incinerated ash contaminated with radioactive substances can be sufficiently decontaminated in a short time, adverse effects on the environment can be reduced and safety can be improved. Thereby, regeneration and reuse of contaminated soil or contaminated incineration ash can be promoted.
本発明の汚染土壌又は汚染焼却灰の除染方法を図１に示す。図１に示すように、本発明は、放射性物物質で汚染された土壌又は焼却灰を回収又は捕集する工程Ｓ１と、該回収又は捕集する工程後の土壌又は焼却灰を室温又は加温下で機械的に粉砕する粉砕工程Ｓ２と、該粉砕工程後の土壌又は焼却灰を水洗する水洗工程Ｓ４と、前記水洗後の土壌又は焼却灰から前記放射性物質を含有する水を分離して回収する分離回収工程Ｓ５とを有することを基本構成とする。さらに、粉砕工程Ｓ２と水洗工程Ｓ４の間に、粗粒子を選別する選別工程Ｓ３を導入することが好ましい。粉砕工程Ｓ２において十分に粉砕しきれないで残存する粗粒子は、選別工程Ｓ３を経由することによって取り除かれる。図１に示すＳ１〜Ｓ５の工程の中で、捕集工程後の土壌又は焼却灰を室温又は加温下で機械的に粉砕する粉砕工程Ｓ２を有することが本発明の大きな特徴である。本発明において、Ｓ２の工程を積極的に採用した理由は以下の通りである。 The decontamination method of the contaminated soil or contaminated incineration ash of the present invention is shown in FIG. As shown in FIG. 1, the present invention collects or collects soil or incinerated ash contaminated with radioactive substances, and room temperature or warms the soil or incinerated ash after the collecting or collecting step. A pulverization step S2 for mechanically pulverizing under water, a rinsing step S4 for rinsing the soil or incinerated ash after the pulverization step, and separating and recovering water containing the radioactive substance from the washed soil or incinerated ash And having a separation and recovery step S5. Furthermore, it is preferable to introduce a selection step S3 for selecting coarse particles between the pulverization step S2 and the water washing step S4. In the pulverization step S2, the coarse particles remaining without being sufficiently pulverized are removed by passing through the selection step S3. Among the steps S1 to S5 shown in FIG. 1, it is a major feature of the present invention that it has a crushing step S2 for mechanically crushing the soil or incinerated ash after the collecting step at room temperature or under heating. In the present invention, the reason why the step S2 is positively employed is as follows.
何らかの要因で原子力発電所から飛散した放射性物質は、周囲の環境に沈降した後、雨水等とともに流出する他にも、樹木の葉、落ち葉又は土壌に残存している。残存した放射性物質、特に人体に大きな悪影響を与えるセシウム（１３７Ｃｓ等）は本来、水に溶けると考えられていたが、土壌の表層に留まっている他、落ち穂（落ち葉）にも粒子として付着していることが分かった。この粒子状物質は、松葉や土壌をイメージングプレート（ＩＰ）による放射能の２次元分布測定を行った結果、確認されたものである。ここで、ＩＰは、光輝尽性蛍光体（ＢａＦＢｒ）のＩＰにエネルギー（放射線）を照射すると、発光中心が準安定状態（励起状態）になり、レーザー光によりエネルギー（波長の長い光）を加え、基底状態（安定状態）に戻るときに発する光を読み取るものであり、それによって放射能２次元分布を測定することができる。 The radioactive material scattered from the nuclear power plant for some reason settles in the surrounding environment and then flows out with rainwater etc., and also remains in the leaves, fallen leaves or soil of the trees. Originally remaining radioactive material, cesium (137 Cs, etc.), particularly of its significant impact on the human body, was considered to dissolve in water, in addition to remains on the surface layer of the soil, also deposited as particles Ochibo (fallen leaves) I found out. This particulate matter has been confirmed as a result of measuring the two-dimensional distribution of radioactivity on pine needles and soil using an imaging plate (IP). Here, when the IP of the photostimulable phosphor (BaFBr) is irradiated with energy (radiation), the emission center becomes a metastable state (excited state), and energy (light having a long wavelength) is added by laser light. The light emitted when returning to the ground state (stable state) is read, whereby the two-dimensional distribution of radioactivity can be measured.
仮に、松葉や土壌に残留する放射性物質が水溶性であれば、前記のＩＰ測定において松葉全体或いは土壌全体が黒色化する結果が得られるはずである。しかし、実際の測定では点状の線源が観測されており、粒子状物質が依然として残留することが確認された。従来の除染方法においても１３７Ｃｓは非水溶性になることが知られており、その原因は、例えば、土壌中に存在するゼオライト様物質に吸着するためであると考えられていた。しかしながら、上記のＩＰ測定によれば、１３７Ｃｓ等の放射性物質は水溶性であるにも関わらず、汚染された松葉表面や土壌中で数１０μｍ程度の顆粒状で存在するために非水溶性となるのではないかと考えられる。したがって、従来の方法によって土壌や焼却灰を水洗しても除染効果が十分に得られていないという実情は、この顆粒状物質の存在が大きく関係しているのではないかとの考察に至った。 If the radioactive substance remaining in the pine needles and the soil is water-soluble, a result of blackening the whole pine needles or the whole soil should be obtained in the IP measurement. However, in the actual measurement, a point-like radiation source was observed, and it was confirmed that the particulate matter still remained. In the conventional decontamination method, it is known that 137 Cs becomes water-insoluble, and the cause is considered to be, for example, because it is adsorbed on a zeolite-like substance existing in soil. However, according to the above IP measurement, although radioactive substances such as 137 Cs are water-soluble, they exist in the form of granules of about several tens of μm on the contaminated pine needle surface and soil, so that they are water-insoluble. It is thought that it becomes. Therefore, the fact that the decontamination effect was not sufficiently obtained even if the soil and incinerated ash were washed with water by the conventional method led to the consideration that the existence of this granular material might be greatly related. .
顆粒状１３７Ｃｓは大気中に放出され、土壌やその他の酸化されやすい環境に留まることで酸化が促進される。酸化Ｃｓは水溶性であるため、酸化が進行すれば、顆粒状１３７Ｃｓは表面から少しずつ溶解し、土壌や植物に移行する。１３７Ｃｓ粒子の表面積が多くなれば、酸化はさらに進むため水溶解性が増し、水洗による１３７Ｃｓの除染効果を大幅に向上できる。本発明は、このような従来にはない新しい知見に基づいてなされたものであり、顆粒状粒子の表面積を増やし、酸化を促進させるために、Ｓ２の工程である顆粒状放射性物質の機械的な粉砕工程を積極的に取り入れる。 Granular 137 Cs is released into the atmosphere, and oxidation is promoted by staying in soil and other oxidizable environments. Since oxidized Cs is water-soluble, if the oxidation proceeds, granular 137 Cs is gradually dissolved from the surface and transferred to soil and plants. If the surface area of the 137 Cs particles is increased, the oxidation further proceeds and the water solubility is increased, and the decontamination effect of 137 Cs by washing with water can be greatly improved. The present invention has been made on the basis of such a new finding that has not existed in the past. In order to increase the surface area of granular particles and promote oxidation, the mechanical activity of the granular radioactive substance, which is the step of S2, is described. Actively incorporate the grinding process.
また、１３７Ｃｓはβ崩壊することでＢａになるが、１３７Ｃｓがβ崩壊する度にＣｓ（＋）とＢａ（＋＋）の結合電子状態の差で顆粒状粉末の内側にクラックが入りやすくなる。これに、本発明のＳ２の工程である機械的な粉砕工程による物理的衝撃を加えれば、顆粒は壊れ小さくなる。それによって、顆粒の表面積が増大し表面酸化が進むため、１３７Ｃｓが土壌から外れ、従来法よりも効率的な除染が可能となるだけでなく、確実な除染によって放射線量の大幅な低減を図ることができる。 In addition, 137 Cs becomes Ba by β-decay, but every time 137 Cs undergoes β-decay, cracks are easily generated inside the granular powder due to the difference in the coupled electronic state between Cs (+) and Ba (++). . If a physical impact is applied to the mechanical crushing process, which is the process of S2 of the present invention, the granules are broken and become smaller. As a result, the surface area of the granule increases and surface oxidation proceeds, so that 137 Cs is removed from the soil, allowing not only more efficient decontamination than conventional methods, but also a significant reduction in radiation dose due to reliable decontamination. Can be achieved.
本発明においては、顆粒状１３７Ｃｓの表面酸化を促進させるために、機械的な粉砕工程Ｓ２によってその表面積を増やすだけでなく、Ｓ２の粉砕工程を酸化剤の存在下で行うことによって酸化反応に拍車をかけることができ、除染の一層の高効率化が図れる。本発明に使用する酸化剤としては、オゾン、過酸化水素、酸素、塩素酸、過塩素酸及び過マンガン酸カリウムからなる群の少なくとも１つを使用する。これらの酸化剤の中で、過酸化水素、塩素酸、過塩素酸及び過マンガン酸カリウムは、通常、水溶液として使用される。水溶液の濃度は、除染効率、粉砕処理時間及び処理量等に応じて、酸化剤の量を土壌もしくは焼却灰に対して０．１〜５重量％の範囲になるように調整する。 In the present invention, in order to promote the surface oxidation of granular 137 Cs, not only the surface area is increased by the mechanical pulverization step S2, but also the oxidation reaction is performed by performing the pulverization step of S2 in the presence of an oxidizing agent. Spurs can be added, and the efficiency of decontamination can be further increased. As the oxidizing agent used in the present invention, at least one of the group consisting of ozone, hydrogen peroxide, oxygen, chloric acid, perchloric acid and potassium permanganate is used. Among these oxidizing agents, hydrogen peroxide, chloric acid, perchloric acid and potassium permanganate are usually used as aqueous solutions. The concentration of the aqueous solution is adjusted so that the amount of the oxidizing agent is in the range of 0.1 to 5% by weight with respect to the soil or the incinerated ash according to the decontamination efficiency, the pulverization time, and the treatment amount.
本発明に使用する酸化剤としては、土壌や焼却灰への影響を最小限にできることから、上記の酸化剤の中で、金属元素を含まないオゾン、過酸化水素、酸素、塩素酸、過塩素酸が好ましい。さらに、土壌や焼却灰のｐＨ変動を抑制するという観点から、オゾン、過酸化水素、酸素がより好ましい。 As the oxidant used in the present invention, since the influence on the soil and incinerated ash can be minimized, among the above oxidants, ozone, hydrogen peroxide, oxygen, chloric acid, perchlorine that does not contain a metal element. Acid is preferred. Furthermore, ozone, hydrogen peroxide, and oxygen are more preferable from the viewpoint of suppressing pH fluctuations of soil and incinerated ash.
本発明においては、図１に示すように、粉砕工程Ｓ２と水洗工程Ｓ４の間に、さらに、粉砕工程後の土壌又は焼却灰から粗粒子を選別する選別工程Ｓ３を採用する理由は以下の通りである。選別工程Ｓ３は、粉砕工程Ｓ２において、機械的な処理能力や処理時間等の観点から顆粒状粒子のすべてを微粒子に粉砕することは困難であり、粉砕しきれないで残存する粗粒子を取り除くために行うものである。粗粒子は、その内部に酸化されていない１３７Ｃｓの存在する量が多いため、後に行う水洗工程Ｓ４において除染効果が十分に得られないという問題がある。しかし、粗粒子の選別工程Ｓ３によって、土壌又は焼却灰の除染漏れを回避することができる。また、粉砕工程Ｓ２において処理時間の削減と処理量の増大を行う場合でも、除染が十分にされていない粗粒子は、選別工程Ｓ３によってあらかじめ選別及び分別されるため、確実な除染効果が安定して得られる。それによって、除染工程のスループットを向上させることができる。 In the present invention, as shown in FIG. 1, the reason for adopting a selection step S3 for selecting coarse particles from the soil or incinerated ash after the pulverization step between the pulverization step S2 and the water washing step S4 is as follows. It is. In the pulverization step S2, the selection step S3 is difficult to pulverize all of the granular particles into fine particles from the viewpoint of mechanical processing capacity, processing time, etc., and removes coarse particles that remain without being pulverized. To do. Since the coarse particles have a large amount of 137 Cs that is not oxidized in the interior thereof, there is a problem that the decontamination effect cannot be sufficiently obtained in the subsequent washing step S4. However, the coarse particle sorting step S3 can avoid soil or incineration ash decontamination leakage. Further, even when the processing time is reduced and the processing amount is increased in the pulverization step S2, coarse particles that are not sufficiently decontaminated are sorted and sorted in advance by the sorting step S3. Obtained stably. Thereby, the throughput of the decontamination process can be improved.
以上のように、本発明の除染方法は、上記のＳ１〜Ｓ２及びＳ４〜Ｓ５の工程、さらに、除染効果の一層の向上を図るために上記Ｓ３の工程を加えたＳ１〜Ｓ５の工程に基づく処理を行って放射性物質を含有する水を分離回収する。分離回収工程の後に得られる水溶液及び残土、残焼却灰は、図１に示すＳ６及びＳ７〜Ｓ９の２つの工程フローに分けて、それぞれ除染処理を行う。 As described above, the decontamination method of the present invention includes the steps S1 to S5 in which the steps S1 to S2 and S4 to S5 are added, and the step S3 is added in order to further improve the decontamination effect. The water containing a radioactive substance is separated and recovered by performing a treatment based on the above. The aqueous solution, the residual soil, and the residual incinerated ash obtained after the separation and recovery step are divided into two process flows of S6 and S7 to S9 shown in FIG.
分離回収工程Ｓ５を経由して分離又は濾過された水溶液は、放射性物質を含有する水、すなわち、土壌又は焼却灰が含まれる放射性物質を抽出した後の水として捕集される（工程Ｓ６）。補修後の放射性物質を含有する水は、放射量測定の結果、放射線量が低い場合には、図１に示すように、水洗工程Ｓ４に戻して水洗用として再利用する。また、放射線量が高い場合には、隔離した場所に保管、貯蔵する方法が一般的にとられる。或いは、処理コストはやや高くなるものの、放射性物質を含有する水から放射性物質だけを精製凝縮する方法を採用しても良い。放射性物質の精製凝縮物は、従来の放射性物質の処理法と同様に、ガラス化したものをコンクリート等の放射線遮蔽物内に保管、貯蔵することができる。 The aqueous solution separated or filtered through the separation / recovery step S5 is collected as water containing a radioactive substance, that is, water after extracting a radioactive substance containing soil or incinerated ash (step S6). As shown in FIG. 1, the water containing the repaired radioactive substance is returned to the washing step S4 and reused for washing as shown in FIG. 1 when the radiation dose is low. Further, when the radiation dose is high, a method of storing and storing in an isolated place is generally used. Alternatively, a method of purifying and condensing only the radioactive substance from the water containing the radioactive substance may be adopted although the processing cost is slightly increased. The purified condensate of the radioactive material can be stored and stored in a radiation shielding material such as concrete, in the same manner as conventional radioactive material processing methods.
また、Ｓ７の工程で回収又は補修される残土、残焼却灰は、Ｓ８の工程において放射線量測定を行い、放射線量が許容値以下か否かの判定を行う。放射線量の判定に応じて、残土又は残焼却灰は、Ｓ９の工程による再生又は再利用、又はＳ２〜Ｓ８の工程による再処理を行うか否かを決める。Ｓ７〜Ｓ９の工程については、後述して説明する。 Moreover, the residual soil and the remaining incinerated ash collected or repaired in the step S7 are subjected to radiation dose measurement in the step S8 to determine whether the radiation dose is equal to or less than an allowable value. Depending on the determination of the radiation dose, the residual soil or residual incinerated ash determines whether or not to regenerate or reuse in the step S9 or reprocess in the steps S2 to S8. Steps S7 to S9 will be described later.
次に、図１に示す本発明による放射性物質除染方法の工程を具体的に説明する。 Next, the steps of the radioactive substance decontamination method according to the present invention shown in FIG. 1 will be described in detail.
（１）汚染された土壌又は焼却灰の回収又は捕集（工程Ｓ１）
放射性物物質で汚染された土壌は、汚染の程度が高い表層部分を手動で、又は油圧ショベル等の重機による切削装置や剥離装置を用いて除去又は剥離する。剥離装置は、植物や水溶性又は水分散性の高分子化合物を用いて土壌の表層を固定した後、剥離操作を行うための装置である。このようにして除去又は剥離された土壌は回収又は捕集した後、後の粉砕工程Ｓ２を行う場所へ輸送する。回収又は捕集する土壌の量が多くない場合は、粉砕工程Ｓ２は土壌の回収又は捕集する場所の傍で行っても良い。なお、本発明の処理対象物である土壌とは、汚染された落ち葉や腐葉土等を有する森林土壌をも含む。
(1) Collection or collection of contaminated soil or incinerated ash (Step S1)
The soil contaminated with the radioactive material is removed or peeled off by using a cutting device or a peeling device by a heavy machine such as a hydraulic excavator manually or by using a heavy machinery such as a hydraulic excavator. The peeling device is a device for performing a peeling operation after fixing the surface layer of soil using a plant or a water-soluble or water-dispersible polymer compound. The soil removed or peeled in this way is collected or collected, and then transported to a place where the subsequent grinding step S2 is performed. When the amount of soil to be collected or collected is not large, the crushing step S2 may be performed near the place where the soil is collected or collected. In addition, the soil which is a process target object of this invention also includes the forest soil which has a contaminated fallen leaf, humus, etc.
焼却灰は、放射性物質で汚染されたゴミ、放置物、落ち葉等を焼却場で焼却した後の灰であり、放射性物質が凝集して高い放射線量を有する。この焼却灰は、水蒸気等の影響により凝集した粗粒子として存在する場合があり、単純な水洗工程では除染効果が十分に得られていなかった。そのため、焼却灰は、通常、隔離した場所に集めて保管、貯蔵されているが、処理量が膨大であり、保管、貯蔵場所の確保が大きな問題となっていた。本発明では、この問題を解決するための除染方法であり、凝集物を含む焼却灰を焼却場からプラスチック製のフレコン袋等を用いて回収又は捕集する。 Incineration ash is ash after incineration of garbage, abandoned items, fallen leaves, etc. contaminated with radioactive substances at an incineration site, and the radioactive substances aggregate and have a high radiation dose. This incinerated ash may exist as coarse particles aggregated due to the influence of water vapor or the like, and the decontamination effect has not been sufficiently obtained by a simple water washing process. Therefore, incineration ash is usually collected and stored in an isolated place, but the processing amount is enormous, and securing the storage and storage place has been a big problem. In this invention, it is a decontamination method for solving this problem, and incineration ash containing agglomerates is collected or collected from an incineration site using a plastic flexible container bag or the like.
（２）機械的な粉砕（工程Ｓ２）
上記のＳ１の工程で回収又は補修された土壌又は焼却灰は、１３７Ｃｓ等の顆粒状放射性物質の表面酸化を促進させるために、表面積を増やすための機械的な粉砕を行う。土壌又は焼却灰の粉砕は、通常の粉砕法によって行う。例えば、複数の羽を有するロータの回転を利用するロータ回転式粉砕機（粉砕効率を上げるためにグラインダを備えるものを含む）、ハンマーのスイングや回転を利用するハンマー式粉砕機、圧縮空気と遠心力を利用する衝撃式粉砕機、衝撃力とせん断による摩砕力を利用する超遠心粉砕機、及びボールを内包する容器を回転撹拌するボールミル粉砕機の何れかを用いて行う。本発明は、土壌又は焼却灰の飛散を抑え、且つ、顆粒を粉砕した後の微粉の平均粒径をより小さくでき、さらに湿式粉砕が可能なことから、ボールミルを用いて回転撹拌を行うボールミル粉砕機による粉砕方法が好ましい。本発明で使用するボールミルのボールの直径は２０〜５０ｍｍのものを使用する。
(2) Mechanical grinding (step S2)
The soil or incinerated ash collected or repaired in the above step S1 is mechanically pulverized to increase the surface area in order to promote surface oxidation of granular radioactive substances such as 137 Cs. The soil or incinerated ash is pulverized by a normal pulverization method. For example, a rotor rotary crusher that uses the rotation of a rotor having a plurality of blades (including those equipped with a grinder to increase crushing efficiency), a hammer type crusher that uses a swing or rotation of a hammer, compressed air and centrifugal An impact type pulverizer that uses force, an ultracentrifugal pulverizer that uses impact force and shearing force, and a ball mill pulverizer that rotates and stirs a container containing balls are used. The present invention suppresses the scattering of soil or incinerated ash, and can further reduce the average particle size of the fine powder after pulverizing the granules, and further enables wet pulverization. A pulverizing method using a machine is preferred. The ball mill used in the present invention has a ball diameter of 20 to 50 mm.
粉砕工程Ｓ２は、通常、室温又は加温下で行われる。Ｓ１の工程で回収又は捕集される土壌又は焼却灰において、水分含有量が少なく乾燥状態に近いものであれば、室温で機械的な粉砕を行うことができ、装置ランニングコストの点からも好ましい。しかし、水分量が多く、粘ついたり汚泥状になっているものは、室温での処理では粉砕が難しいため、加温によって含まれる水分を蒸発させながら撹拌による粉砕を行っても良い。加温時の温度は３０〜７０℃の範囲で調整できるが、粉砕効率と装置の耐久性の点から４０〜５０℃の範囲が好ましい。 The pulverization step S2 is usually performed at room temperature or under heating. In the soil or incinerated ash collected or collected in the step of S1, if the water content is low and close to a dry state, mechanical pulverization can be performed at room temperature, which is preferable from the viewpoint of apparatus running cost. . However, a thick, sludge-like material having a high water content is difficult to be pulverized by treatment at room temperature. Therefore, pulverization by stirring may be performed while evaporating water contained by heating. Although the temperature at the time of heating can be adjusted in the range of 30-70 degreeC, the range of 40-50 degreeC is preferable from the point of grinding | pulverization efficiency and the durability of an apparatus.
本発明の粉砕工程で使用する粉砕機は、土壌又は焼却灰に含まれる放射性物質の飛散や揮散を防ぐため、密閉式のものが好ましい。加温しながら粉砕を行う場合は、水分等の揮発成分の蒸発を容易にするために、粉砕機に微細な多孔質の穴やメッシュを設けることができる。また、土壌又は焼却灰を微細な穴やメッシュを有する容器に入れた後、その容器の上部等の所定の位置に蒸気を逃すための排気口を設けた密閉式の別の容器に入れ、前記の微細な穴やメッシュを有する容器だけを回転撹拌できるような構成を有する粉砕機を使用しても良い。 The crusher used in the crushing process of the present invention is preferably a hermetic type in order to prevent scattering or volatilization of radioactive materials contained in soil or incinerated ash. When pulverizing while heating, a fine porous hole or mesh can be provided in the pulverizer to facilitate evaporation of volatile components such as moisture. In addition, after putting soil or incinerated ash in a container having a fine hole or mesh, put it in another sealed container provided with an exhaust port for releasing steam at a predetermined position such as the upper part of the container, You may use the grinder which has a structure which can rotate and stir only the container which has these fine holes and meshes.
粉砕工程Ｓ２は、本発明の除染方法において鍵となる工程であり、土壌又は焼却灰の粉砕後の粒子径が除染効率と除染効果に大きな影響を及ぼす。本発明の効果を奏するためには、土壌、放射性物物質で汚染された土壌又は焼却灰は平均粒径が粉砕前の平均粒径の１／３以下となるように粉砕することが好ましい。ここで、平均粒径は、日本工業規格ＪＩＳ Ａ １２０４に基づいてふるい分級によって得られる粒径加積曲線において、重量比が５０％にあたる粒径Ｄ５０に該当するものとして定義する。粉砕後の平均粒径が粉砕前のものと比べて１／３を超えると、粉砕が十分に行われていないことを意味し、除染の効果が小さく本発明の目的である確実な除染を行うことが難しい。粉砕後の平均粒径を粉砕前の平均粒径の１／３以下になるまで粉砕することによって、放射性物質の減少割合を２倍以上にすることができる。粉砕前の土壌又は焼却灰は、通常、平均粒径として細礫の粒径に近い１〜４ｍｍを有する。そのため、本発明において、具体的な粉砕後の平均粒径としては、粗砂の粒径に近い１ｍｍ以下、好ましくは０．５ｍｍ以下となるまで粉砕を行うことが好ましい。 The pulverization step S2 is a key step in the decontamination method of the present invention, and the particle size after pulverization of soil or incinerated ash greatly affects the decontamination efficiency and decontamination effect. In order to achieve the effect of the present invention, it is preferable to grind the soil, soil contaminated with radioactive substances, or incinerated ash so that the average particle size is 1/3 or less of the average particle size before pulverization. Here, the average particle size is in the particle size accumulation curve obtained by sieve classification based on the Japanese Industrial Standard JIS A 1204, is defined as the weight ratio corresponds to the particle size D 50 corresponding to 50%. If the average particle size after pulverization exceeds 1/3 compared with that before pulverization, it means that the pulverization is not sufficiently performed, and the decontamination effect is small, which is the object of the present invention. Difficult to do. By reducing the average particle size after pulverization to 1/3 or less of the average particle size before pulverization, the reduction ratio of the radioactive substance can be doubled or more. The soil or incinerated ash before pulverization usually has an average particle diameter of 1 to 4 mm, which is close to the particle size of the fine gravel. Therefore, in this invention, it is preferable to grind | pulverize as a concrete average particle diameter after a grinding | pulverization until it becomes 1 mm or less near the particle diameter of coarse sand, Preferably it becomes 0.5 mm or less.
粉砕機を稼働するための諸条件（粉砕機の容量、ロータやハンマーの回転速度又はボールミルを有する粉砕容器の回転撹拌速度等）は、粉砕後の粒子の平均粒径が所定の値となるように、土壌又は焼却灰の処理量と処理時間に応じて設定することができる。 Various conditions for operating the pulverizer (the capacity of the pulverizer, the rotational speed of the rotor and hammer, the rotational stirring speed of the pulverizing container having a ball mill, etc.) are such that the average particle diameter of the pulverized particles becomes a predetermined value. Furthermore, it can set according to the processing amount and processing time of soil or incineration ash.
上記で述べたように、本発明の粉砕工程は、顆粒状１３７Ｃｓの表面酸化を促進させることによって除染の一層の高効率化を図るために、酸化剤の存在下で行うことが好ましい。本発明で使用する酸化剤としては、オゾン、過酸化水素、酸素、塩素酸、過塩素酸及び過マンガン酸カリウムからなる群の少なくとも１つからなり、それらの１種又は２種以上を使用することができる。 As described above, the pulverization step of the present invention is preferably performed in the presence of an oxidizing agent in order to further increase the efficiency of decontamination by promoting the surface oxidation of granular 137 Cs. The oxidizing agent used in the present invention is composed of at least one of the group consisting of ozone, hydrogen peroxide, oxygen, chloric acid, perchloric acid and potassium permanganate, and one or more of them are used. be able to.
上記の酸化剤は、あらかじめ粉砕を行う前に土壌又は焼却灰に混入させても良いし、粉砕工程の途中で加えても良い。また、酸化剤の混入は、１回だけではなく、数回に分けて行っても良い。水等の希釈剤を含まない酸化剤そのものの含有量は、土壌又は焼却灰の１００重量部に対して１〜３重量部である。含有量が１重量部未満では、酸化剤としての効果が期待できず、また、３重量部を超えると、酸化剤としての効果が飽和するだけでなく、汚染された土壌又は焼却灰の処理量が少なくなる。 The above oxidizing agent may be mixed in the soil or incinerated ash before pulverization, or may be added during the pulverization step. Further, the mixing of the oxidizing agent may be performed not only once but also in several times. Content of the oxidizing agent itself which does not contain diluents, such as water, is 1-3 weight part with respect to 100 weight part of soil or incinerated ash. If the content is less than 1 part by weight, the effect as an oxidant cannot be expected. If the content exceeds 3 parts by weight, not only the effect as an oxidant is saturated but also the amount of contaminated soil or incinerated ash treated. Less.
（３）粗粒子の選別（工程Ｓ３）
上記の粉砕工程Ｓ２の後に、粉砕しきれないで残存する粗粒子を取り除くために、土壌又は焼却灰から粗粒子の選別を行う。この選別工程によって、酸化されていない１３７Ｃｓを内部に多く含有する粗粒子を除去できるため、水洗による除染効果を確実なものとすることができる。粗粒子の選別は、大量の土壌又は焼却灰の処理が簡便にでき、且つ、処理コストを低く抑えることができることから、通常は、所定の呼び（目開き）寸法を有する篩を用いる。選別する土壌や焼却灰の量が少ない場合には、篩による方法の他にも、遠心分離機等を使用してもよい。
(3) Selection of coarse particles (step S3)
After the pulverization step S2, the coarse particles are selected from the soil or incinerated ash in order to remove coarse particles that cannot be pulverized and remain. By this sorting step, coarse particles containing a large amount of unoxidized 137 Cs can be removed, so that the decontamination effect by washing with water can be ensured. Since the selection of coarse particles can easily process a large amount of soil or incinerated ash and can keep the processing cost low, a sieve having a predetermined nominal (opening) size is usually used. If the amount of soil or incineration ash to be selected is small, a centrifuge may be used in addition to the method using a sieve.
粗粒子の選別工程Ｓ３は、本発明の除染方法において、機械的な粉砕工程Ｓ２に加えて、確実な除染を行うための鍵となる工程であり、粉砕された土壌又は焼却灰に含まれる粗粒子の粒子径が除染の効率と効果に大きな影響を及ぼす。本発明の効果を奏するために、粗粒子は、最小粒径として１ｍｍを超えるものが選別されることが好ましい。最小粒径が１ｍｍを超える粗粒子の選別は、例えば、呼び寸法が１ｍｍ（１６メッシュ）以下の篩を用いて行うことができる。選別後の土壌又は焼却灰に最小粒径が１ｍｍを超える粗粒子が残存すると、粗粒子内に存在する数１０μｍの顆粒状１３７Ｃｓの量が多くなるため除染が不十分となり、本発明の目的である確実な除染を行うことが難しい。 The coarse particle sorting step S3 is a key step for reliable decontamination in addition to the mechanical crushing step S2 in the decontamination method of the present invention, and is included in the crushed soil or incinerated ash. The particle size of the coarse particles greatly affects the efficiency and effect of decontamination. In order to achieve the effect of the present invention, it is preferable to select coarse particles having a minimum particle size exceeding 1 mm. The selection of coarse particles having a minimum particle size exceeding 1 mm can be performed using, for example, a sieve having a nominal size of 1 mm (16 mesh) or less. When coarse particles having a minimum particle size exceeding 1 mm remain in the sorted soil or incinerated ash, the amount of granular 137 Cs of several tens of μm present in the coarse particles is increased, resulting in insufficient decontamination. It is difficult to perform decontamination that is the purpose.
本発明において選別工程Ｓ３で選別及び分別された粗粒子は、図１に示すように、粉砕工程Ｓ２に戻して粉砕を再度行うことができる。その場合、選別及び分別された粗粒子は、選別工程Ｓ３を行った後、直ちに粉砕工程Ｓ２へ戻す方法でも良いし、２回以上の選別工程Ｓ３を経て捕集した粗粒子をまとめた状態で粉砕工程Ｓ２へ戻しても良い。また、除染処理時間の短縮化や除染工程の簡略化等を行うために、選別及び分別された粗粒子を直ちに粉砕工程Ｓ２に戻す必要がない場合には、該粗粒子を隔離した場所に所定の期間だけ保管又は貯蔵することができる。その場合にも、まとまった量の粗粒子は、後で粉砕工程Ｓ２に投入しても良い。このようにして、水洗工程Ｓ４で水洗処理を行う土壌又は焼却灰は残存する粗粒子の量が大幅に低減しているため、水洗による土壌又は焼却灰の除染漏れを回避できる効果が格段に向上する。 In the present invention, the coarse particles sorted and sorted in the sorting step S3 can be returned to the pulverizing step S2 and pulverized again as shown in FIG. In that case, the sorted and sorted coarse particles may be returned to the pulverization step S2 immediately after the sorting step S3, or the coarse particles collected through two or more sorting steps S3 are collected. You may return to grinding | pulverization process S2. In addition, in order to shorten the decontamination processing time, simplify the decontamination process, and the like, if it is not necessary to immediately return the sorted and sorted coarse particles to the pulverization step S2, the place where the coarse particles are isolated Can be stored or stored for a predetermined period of time. Even in that case, a large amount of coarse particles may be added to the pulverization step S2 later. In this way, the amount of coarse particles remaining in the soil or incinerated ash subjected to the water washing process in the water washing step S4 is greatly reduced, so that the effect of avoiding the decontamination leakage of the soil or incinerated ash due to the water washing is remarkably improved. improves.
（４）水洗（工程Ｓ４）
Ｓ２又はＳ３の工程の後に得られる土壌又は焼却灰の粉砕粒子は、放射性物質の溶解性、取扱い性や作業性並びに周辺への環境負荷の低減を考慮して、水又は水を主成分とする水系媒体で洗浄する。本発明において使用する水を主成分とする水系媒体は、水が８０質量％以上、好ましくは９０質量％以上、さらに好ましくは９５質量％以上を占める媒体である。水以外には、例えば、水溶性のメチルアルコール、エチルアルコール、２プロパノール等のアルコール類、ジエチルエーテル、テトラヒドロフラン等のエーテル類又はアセトン、メチルエチルケトン、シクロヘキサノン等のケトン類の溶媒を少量配合して使用してもよい。これらの溶媒の中で、人体に対する影響と環境負荷が少ないするためにエチルアルコールが好ましい。
(4) Washing with water (step S4)
Soil or incinerated ash crushed particles obtained after the step S2 or S3 are mainly water or water in consideration of the solubility of radioactive materials, handling and workability, and reduction of environmental load on the surroundings. Wash with aqueous medium. The aqueous medium mainly composed of water used in the present invention is a medium in which water accounts for 80% by mass or more, preferably 90% by mass or more, and more preferably 95% by mass or more. In addition to water, for example, water-soluble alcohols such as methyl alcohol, ethyl alcohol, and 2-propanol, ethers such as diethyl ether and tetrahydrofuran, or ketones such as acetone, methyl ethyl ketone, and cyclohexanone are used in a small amount. May be. Among these solvents, ethyl alcohol is preferable because it has less influence on the human body and less environmental burden.
水洗工程Ｓ３は、容器中で粉砕後の土壌又は焼却灰を水又は水系媒体に浸漬させるだけで大きな除染効果が得られる。それ以外にも、土壌又は焼却灰の粒子と水又は水系媒体との接触を向上させて両者を密接させるために、ミキサー中で混ぜたり、容器中に攪拌機を備えて撹拌を行うことができる。これらの処理は、水洗工程において処理時間を短くでき、効率的な除染方法を構築することができるため、本発明において好ましい水洗方法である。ここで、水洗時に使用する水又は水系媒体の量は、粉砕後の土壌又は焼却灰の量に対して、質量比で１〜５倍量が好ましく、処理速度と処理量の観点から３〜５倍量がより好ましい。 In the washing step S3, a large decontamination effect can be obtained only by immersing the ground soil or incinerated ash in water or an aqueous medium in a container. In addition, in order to improve contact between the particles of soil or incinerated ash and water or an aqueous medium so as to bring them into close contact with each other, they can be mixed in a mixer or stirred with a stirrer in a container. These treatments are preferable washing methods in the present invention because the treatment time can be shortened in the washing step and an efficient decontamination method can be constructed. Here, the amount of water or aqueous medium used at the time of washing is preferably 1 to 5 times by mass with respect to the amount of soil or incinerated ash after pulverization, and 3 to 5 in terms of processing speed and processing amount. A double amount is more preferred.
水洗工程Ｓ３は、通常、室温で行うが、３０〜６０℃に加温して行うことができる。また、水洗処理は、通常、上方が解放した容器を用いて行うが、水若しくは水系溶媒の揮発又は放射性物質の飛散を防ぐために、密閉容器や準密閉容器を用いて水洗処理を行っても良い。 The water washing step S3 is usually performed at room temperature, but can be performed by heating to 30 to 60 ° C. In addition, the water washing treatment is usually performed using a container opened at the top, but the water washing treatment may be performed using a sealed container or a semi-sealed container in order to prevent volatilization of water or an aqueous solvent or scattering of radioactive substances. .
（５）分離回収（工程Ｓ５及びＳ６）
水洗工程Ｓ４の後に捕集された土壌又は焼却灰は、放射性物質を含有する水を分離回収するための処理を行う（工程Ｓ５）。この処理後に、分離又は濾過された水溶液は、工程６において捕集される。本発明において、前記放射性物質を含有する水とは、主に放射性物質を含有する水溶液を意味するが、分離回収できなかった微粒子や細かな汚泥を含有する水溶液をも含んでいる。前記前記放射性物質を含有する水を除いた残土又は残焼却灰は、後に続く工程によって再生又は再利用される。
(5) Separation and recovery (Steps S5 and S6)
The soil or incinerated ash collected after the water washing step S4 is subjected to a treatment for separating and recovering water containing the radioactive substance (step S5). After this treatment, the separated or filtered aqueous solution is collected in step 6. In the present invention, the water containing a radioactive substance mainly means an aqueous solution containing a radioactive substance, but also includes an aqueous solution containing fine particles and fine sludge that could not be separated and recovered. The residual soil or residual incinerated ash excluding the water containing the radioactive substance is regenerated or reused in a subsequent process.
分離回収工程Ｓ５は主に濾過法によって行うが、それ以外にも、ハイドロサイクロン法、デカンテーション法及び遠心分離法の何れかの方法、又はこれらの方法の２以上を組合わせて行っても良い。 The separation / recovery step S5 is mainly performed by a filtration method, but in addition, any one of the hydrocyclone method, the decantation method, and the centrifugal separation method, or a combination of two or more of these methods may be performed. .
濾過法は公知の濾過システムを利用でき、ろ紙又はプラスチック製フィルターを用いて常圧、真空、加圧の何れの方法で行うことができる。また、限外濾過法を使用しても良い。ろ紙又はプラスチック製フィルターは、数１０μｍ以下の径を有する粒子を濾過できるもので有れば良く、濾過能力、処理量及び処理時間に応じて適当なものを選ぶことができる。これらの特性のバランスをとるために、ろ紙又はフィルターの孔径は０．５〜２０μｍの範囲が好ましい。 As the filtration method, a known filtration system can be used, and it can be performed by any method of normal pressure, vacuum, and pressure using a filter paper or a plastic filter. Further, an ultrafiltration method may be used. The filter paper or plastic filter is not limited as long as it can filter particles having a diameter of several tens of μm or less, and an appropriate filter can be selected according to the filtration capacity, the processing amount, and the processing time. In order to balance these characteristics, the pore size of the filter paper or filter is preferably in the range of 0.5 to 20 μm.
上記のデカンテーション法は特別な装置や設備が不要であるとともに、大量の処理が可能であることから本発明において採用することができる。また、遠心分離法は、処理量にある程度の制約はあるものの、短時間に、且つ高精度で分離回収を行うことができるため、濾過法及びデカンテーション法と同様に本発明において有用な方法である。 The above decantation method can be employed in the present invention because it does not require a special device or equipment and can perform a large amount of processing. In addition, the centrifugal separation method is useful in the present invention in the same manner as the filtration method and the decantation method because the separation and collection can be performed in a short time and with high accuracy, although there is a certain amount of restriction on the throughput. is there.
本発明の分離回収工程Ｓ５においては、前記の濾過法、デカンテーション法及び遠心分離法の何れかの方法を行う前に、水洗工程Ｓ４で水洗された土壌又は焼却灰の粒子の中で最小粒径１ｍｍを超える粒子、好ましくは１００μｍを超える粒子をあらかじめ篩を用いて取り除くことが好ましい。例えば、土壌又は焼却灰と水溶液の分離を濾過法で行う場合、濾過は孔径が小さく目の細かいろ紙又はフィルターで行われるため、大きな粒子が存在すると濾過効率が低下する。そのため、あらかじめ１ｍｍを超える粒子、好ましくは１００μｍを超える粒子を篩によって取り除いて大きな粒子の土壌又は焼却灰を水溶液から分離した後、篩を通り抜けた粒子と水溶液を目の細かいろ紙又はフィルターで分離する２段階の分離法を採用することによって、濾過効率を向上させることができる。 In the separation and recovery step S5 of the present invention, before performing any of the filtration method, the decantation method, and the centrifugal separation method, the smallest particles among the soil or incinerated ash particles washed in the water washing step S4. It is preferable to remove particles having a diameter exceeding 1 mm, preferably particles exceeding 100 μm, using a sieve in advance. For example, when separation of soil or incinerated ash and an aqueous solution is performed by a filtration method, the filtration is performed with a filter paper or a filter having a small pore size and fine mesh. Therefore, after removing particles larger than 1 mm in advance, preferably particles larger than 100 μm, with a sieve to separate large particles of soil or incinerated ash from the aqueous solution, the particles passing through the sieve and the aqueous solution are separated with a fine filter paper or filter. By employing a two-stage separation method, the filtration efficiency can be improved.
本発明において、上記の粗粒子の選別工程Ｓ３を採用しない場合には、水洗工程Ｓ４で水洗された土壌又は焼却灰の粒子の中に最小粒径１ｍｍを超える粒子が存在しているため、まずこの大きな粒子を取り除く必要がある。これは、酸化されていない１３７Ｃｓを内部に多く含有する粗粒子を除去するためでもある。さらに、最小粒径が１ｍｍ以下で１００μｍを超える粒子を取り除くことができれば、土壌又は焼却灰と水溶液の分離効率を大幅に高めることができる。一方、粗粒子の選別工程Ｓ３を採用する場合には、最小粒径１ｍｍを超えるものが既に選別されて除去されているため、分離回収工程５においては、最小粒径１００μｍを超える粒子をあらかじめ取り除くことによって濾過の効率を高めることができる。最大粒径が１００μｍを超える粒子の選別は、土壌又は焼却灰を含む大量の水を簡便に処理でき、且つ、処理コストを相対的に低くできることから、呼び寸法が１０６μｍ（１４０メッシュ）、１００μｍ（１４９メッシュ）若しくはそれより小さい呼び寸法を有する篩を用いて行う。 In the present invention, when the above coarse particle sorting step S3 is not adopted, since there are particles exceeding the minimum particle size of 1 mm in the soil or incinerated ash particles washed in the water washing step S4, It is necessary to remove these large particles. This is also for removing coarse particles containing a large amount of unoxidized 137 Cs. Further, if particles having a minimum particle diameter of 1 mm or less and exceeding 100 μm can be removed, the separation efficiency between the soil or the incinerated ash and the aqueous solution can be significantly increased. On the other hand, when the coarse particle sorting step S3 is adopted, since particles having a minimum particle size of 1 mm are already sorted and removed, in the separation and recovery step 5, particles having a minimum particle size of 100 μm are removed in advance. Thus, the efficiency of filtration can be increased. The selection of particles having a maximum particle size exceeding 100 μm can easily process a large amount of water containing soil or incinerated ash and can relatively reduce the processing cost. Therefore, the nominal size is 106 μm (140 mesh), 100 μm ( 149 mesh) or smaller sieve size.
最小粒径１００μｍを超える粒子を篩によって取り除く上記の方法は、濾過法だけでなく、ハイドロサイクロン法、デカンテーション法又は遠心分離法の場合にも適用できる。それらの方法の中で、濾過法、デカンテーション法及び遠心分離法の何れかの方法と合わせて適用するときに分離効率の向上に対して大きな効果を得ることができる。 The above method for removing particles having a minimum particle size of 100 μm by a sieve is applicable not only to the filtration method but also to the hydrocyclone method, the decantation method, or the centrifugal separation method. Among these methods, when applied in combination with any of the filtration method, the decantation method, and the centrifugation method, a great effect can be obtained with respect to the improvement of the separation efficiency.
また、本発明においては、上記の分離回収方法の他に、水洗工程Ｓ４及び分離回収工程Ｓ５を連続的に行うために次の方法を採用することもできる。すなわち、上部開放型容器の底面又は中間部にろ紙やフィルターをあらかじめ設置した後、粉砕後の土壌又は焼却灰を前記容器に入れる。その後、前記容器の上方から水又は水系溶媒をシャワー方式で全体に万遍なく連続的に降り注いで、粉砕した土壌又は焼却灰を通過した水又は水系溶媒を容器底面で受けて溜めるか、又は容器底面の下部に受け皿を設ける方法である。後者の場合は、前記容器の底面形状を、例えば、開放部を有するメッシュ状にする。また、別の方法として、粉砕後の土壌又は焼却灰を筒や管に入れて、筒や管の一方の入口から水若しくは水系媒体を連続的に注入して、もう一方の別の出口から流出させる方法等を採用しても良い。その場合、粗粒子の選別工程Ｓ３を行った後に、水洗工程Ｓ４及び分離回収工程Ｓ５からなる連続的な処理を行っても良い。 Further, in the present invention, in addition to the separation and recovery method described above, the following method may be employed in order to continuously perform the water washing step S4 and the separation and recovery step S5. That is, after a filter paper and a filter are installed in advance on the bottom or middle part of the upper open container, the ground soil or incinerated ash is put into the container. Thereafter, water or an aqueous solvent is continuously and uniformly poured from the upper side of the container by a shower method, and the water or aqueous solvent that has passed through the crushed soil or incinerated ash is received and stored at the bottom of the container, or the container In this method, a tray is provided at the bottom of the bottom. In the latter case, the bottom shape of the container is, for example, a mesh shape having an open portion. As another method, pulverized soil or incinerated ash is put into a cylinder or tube, water or an aqueous medium is continuously injected from one inlet of the cylinder or tube, and then discharged from the other outlet. You may employ | adopt the method of making it. In that case, you may perform the continuous process which consists of the water washing process S4 and the separation-and-recovery process S5 after performing the selection process S3 of coarse particles.
（６）残土又は残焼却灰の再生又は再利用（工程Ｓ７〜Ｓ９）
Ｓ５の工程後に得られる残土又は残焼灰はＳ７の工程で回収又は捕集される。その後、回収物又は捕集物はそのまま放射性廃棄物として隔離した場所に保管、貯蔵しても良い。これら残土又は残焼却灰は、Ｓ１〜Ｓ５の工程を有する除染方法によって放射性物質の濃度をかなり低減できるため、そのまま放射性廃棄物として隔離した場所に保管、貯蔵する場合でも、周囲の環境への悪影響を小さくできるだけでなく、従来の除染方法よりも安全性が高くなるため、大きな安心感が得られる。しかしながら、本発明においては、除染後の残土又は残焼灰の再生を速め、再利用を促進するために、さらにＳ８及びＳ９の工程を行うことが好ましい。
(6) Regeneration or reuse of residual soil or residual incineration ash (steps S7 to S9)
The residual soil or residual ash obtained after the step S5 is recovered or collected in the step S7. Thereafter, the collected or collected material may be stored and stored in a place isolated as radioactive waste. These residual soil or residual incinerated ash can significantly reduce the concentration of radioactive material by the decontamination method having the steps S1 to S5. Therefore, even when stored and stored in a place isolated as radioactive waste, Not only can the adverse effects be reduced, but the safety is higher than the conventional decontamination method, so that a great sense of security can be obtained. However, in the present invention, it is preferable to further perform steps S8 and S9 in order to speed up the regeneration of the residual soil or residual burned ash after decontamination and promote the reuse.
上記のＳ７の工程で回収又は捕集された残土、残焼却灰は、Ｓ８の工程において放射線量測定を行い、放射線量が許容値以下か否かの判定を行う。放射線量が所定の許容値以下であると判定されたときは、Ｓ９の工程において、残土又は残焼却灰は回収前又は捕集前の元の場所へ戻すか、場合によっては、埋土として必要とされる別の場所に廃棄する。仮に、放射線量が所定の許容値を超えると判定されたときには、残土又は残焼却灰は粉砕工程Ｓ２に戻されて、Ｓ２〜Ｓ８の工程が放射線量が所定の許容値以下になるまで繰り返される。本発明においては、残土又は焼却灰の放射線量が所定の許容値を超えた場合でも、除染処理量が大幅に増え、それに対応する必要がある場合は、再処理のためにＳ２〜Ｓ８の工程を繰り返す操作を途中で止めても良い。再処理を中断した残土又は焼却灰は、例えばプラスチック製のフレコン袋等に梱包した後、隔離した場所に保管、保存する。また、再処理のためのＳ２〜Ｓ８の工程の中で、粗粒子の選別工程Ｓ３は、土壌又は焼却灰を除染する際の処理量と処理時間に応じて導入するか否かを決めることができる。 The residual soil and residual incinerated ash collected or collected in the step S7 are subjected to radiation dose measurement in the step S8 to determine whether the radiation dose is equal to or less than an allowable value. When it is determined that the radiation dose is less than or equal to the predetermined allowable value, the residual soil or residual incinerated ash is returned to the original location before recovery or before collection in the step of S9, or in some cases required as buried soil Discard it in another place. If it is determined that the radiation dose exceeds a predetermined allowable value, the remaining soil or the remaining incinerated ash is returned to the pulverization step S2, and the steps S2 to S8 are repeated until the radiation dose becomes a predetermined allowable value or less. . In the present invention, even when the radiation amount of the residual soil or incinerated ash exceeds a predetermined allowable value, the decontamination processing amount is greatly increased. You may stop operation which repeats a process on the way. Residual soil or incinerated ash from which reprocessing has been suspended is stored and stored in an isolated place after being packed in a flexible container bag made of plastic, for example. In addition, among the steps S2 to S8 for reprocessing, it is determined whether or not the coarse particle sorting step S3 is to be introduced according to the processing amount and processing time when decontaminating soil or incinerated ash. Can do.
以上のように、本発明の除染方法は、放射性物質で汚染された土壌又は焼却灰の除染を効率良く、且つ、効果的に行うことによって環境への悪影響を低減し、安全性を高めるために、図１に示すＳ１〜Ｓ５の工程を基本構成として、Ｓ６及びＳ７の工程を有する。さらに、汚染土壌又は汚染焼却灰の再生及び再利用を促進するために、Ｓ７〜Ｓ９の工程を有するものである。 As described above, the decontamination method of the present invention reduces the adverse effects on the environment and enhances safety by efficiently and effectively decontaminating soil contaminated with radioactive substances or incinerated ash. For this purpose, the steps S1 to S5 shown in FIG. Furthermore, in order to promote the regeneration and reuse of the contaminated soil or the contaminated incineration ash, steps S7 to S9 are provided.
本発明を実施例によって説明するが、本発明の範囲はこれらの実施例に限定されるものではない。 The present invention will be described with reference to examples, but the scope of the present invention is not limited to these examples.
［実施例１］
本発明の除染方法の効果について、少量スケールで確認実験を行った。１３７Ｃｓを含み、放射線量が１５０，９２０Ｂｑ／ｋｇと測定された土壌の１０ｇを、密閉式のドラム形状を有するＷ−Ｃ粉砕機を用いて室温で６０秒間粉砕した。Ｗ−Ｃ粉砕機には、粒径が１００〜３００μｍのボールミルを混入する。粉砕後の土壌の平均粒径Ｄ５０は５０μｍ以下であり、粉砕前の土壌の平均粒径と比べると、１／４以下に微粉砕されていることが分かった。放射線量は、Ｇｅ半導体検出器（ＣＡＮＢＥＲＡ製）を用いて測定を行い、計数値（Ｃｔｓ／ｓｅｃ／ｇ）からＢｑ／ｋｇに換算した。また、平均粒径Ｄ５０は、ＪＩＳ Ａ １２０４規格に基づいてふるい分析によって得られる粒径加積曲線から求めた。
[Example 1]
The effect of the decontamination method of the present invention was confirmed on a small scale. 10 g of soil containing 137 Cs and having a radiation dose of 150,920 Bq / kg was pulverized for 60 seconds at room temperature using a WC pulverizer having a closed drum shape. A ball mill having a particle size of 100 to 300 μm is mixed in the WC pulverizer. The average particle diameter D 50 of the soil after grinding is at 50μm or less, compared with the average particle size of the soil before grinding was found to be finely ground to 1/4 or less. The radiation dose was measured using a Ge semiconductor detector (manufactured by CANBERA) and converted from a count value (Cts / sec / g) to Bq / kg. The average particle diameter D 50 was determined from the grain size accumulation curve obtained by sieve analysis based on JIS A 1204 standard.
次いで、粉砕した土壌を４００ｍｌの水に２時間浸漬して洗浄した。その後、水に浸漬された土壌を孔径が１０〜１３μｍのろ紙を用いて濾過して乾燥した。 Next, the pulverized soil was washed by immersing it in 400 ml of water for 2 hours. Thereafter, the soil immersed in water was filtered and dried using a filter paper having a pore size of 10 to 13 μm.
濾過及び乾燥の後、ろ紙上の残渣として得られる残土の量は８．５ｇであり、その放射線量は測定の結果、８５０Ｂｑ（１００，０００Ｂｑ／ｋｇ）になった。一方、濾過水は、蒸発乾固した後の残渣について測定した放射線量が４５０Ｂｑ（３００，０００Ｂｑ／ｋｇ）であった。本発明の除染方法によって、濾過後の残渣である残土の放射性物質は約半分（１５０９Ｂｑ→８５０Ｂｑ）に減少することが分かる。なお、放射性物質の収支（ΔＱ）はΔＱ＝１５０９−（８５０＋４５０）＝２０９Ｂｑと誤差が生じているが、これは放射線量の測定誤算又は処理容器等への付着等によるものと考えられる。本実施例における放射線量の単位質量当たりの減衰率は、１５０ｋＢｑ／ｋｇ→１００ｋＢｑ／ｋｇであり、約３３％である。 After filtration and drying, the amount of residual soil obtained as a residue on the filter paper was 8.5 g, and the radiation dose was 850 Bq (100,000 Bq / kg) as a result of measurement. On the other hand, the filtered water had a radiation dose of 450 Bq (300,000 Bq / kg) measured on the residue after evaporation to dryness. By the decontamination method of this invention, it turns out that the radioactive material of the residual soil which is the residue after filtration reduces to about half (1509Bq-> 850Bq). The balance (ΔQ) of the radioactive substance has an error of ΔQ = 1509− (850 + 450) = 209Bq, which is considered to be due to miscalculation of the radiation dose or adhesion to a processing container or the like. The attenuation rate per unit mass of the radiation dose in this example is 150 kBq / kg → 100 kBq / kg, which is about 33%.
［比較例１〜２］
放射線量が８，４４０Ｂｑ／ｋｇ及び１３，２００Ｂｑ／ｋｇと測定された土壌Ａ及び土壌Ｂの各２０ｇについて、Ｗ−Ｃ粉砕機による粉砕処理工程を省略する以外は、実施例１と同じ方法で除染を行った。
[Comparative Examples 1-2]
Except for omitting the pulverization process step by the WC pulverizer for 20 g of soil A and soil B each having a radiation dose of 8,440 Bq / kg and 13,200 Bq / kg, the same method as in Example 1 was used. Decontamination was performed.
上記の土壌Ａ及び土壌Ｂは、それぞれ２００ｍｌの水に８時間浸漬して洗浄した。その後、水に浸漬された土壌を孔径が１３μｍのろ紙を用いて濾過して乾燥した。ここで、土壌Ａ及び土壌Ｂの除染方法を、それぞれ比較例１及び２とする。 The above soil A and soil B were each immersed and washed in 200 ml of water for 8 hours. Thereafter, the soil immersed in water was filtered and dried using a filter paper having a pore size of 13 μm. Here, the decontamination methods of soil A and soil B are referred to as Comparative Examples 1 and 2, respectively.
濾過及び乾燥後、ろ紙上の残渣として得られる土壌Ａ及び土壌Ｂの量は２０ｇであり、その放射線量は測定の結果、それぞれ７，６１８Ｂｑ／ｋｇ及び１２，２５５Ｂｑ／ｋｇになった。比較例１及び２における放射線量の単位質量当たりの減衰率は、それぞれ９．７％及び７．２％である。 After filtration and drying, the amount of soil A and soil B obtained as residues on the filter paper was 20 g, and the radiation doses were 7,618 Bq / kg and 12,255 Bq / kg, respectively, as a result of measurement. The attenuation rates per unit mass of the radiation dose in Comparative Examples 1 and 2 are 9.7% and 7.2%, respectively.
このように、実施例１は、比較例１及び２と比べて、放射線量の単位質量当たりの減衰率が３倍以上となり、粉砕工程によって高い除染効果が得られることが確認できた。また、実施例１と比較例１−２の間で除染処理の総時間を対比すると、水洗工程で使用する水の量が両者で異なるために一概に比較することは困難であるものの、実施例１は比較例１及び２と比べて、総処理時間が約１／４に短縮している。したがって、本発明は、従来法と比べて、効率的で、且つ、確実な除染を行うことができる除染方法となることが期待される。 Thus, in Example 1, compared with Comparative Examples 1 and 2, the attenuation rate per unit mass of the radiation dose was 3 times or more, and it was confirmed that a high decontamination effect was obtained by the pulverization process. Moreover, when the total time of a decontamination process is contrasted between Example 1 and Comparative Example 1-2, since the quantity of the water used at a water-washing process differs in both, it is difficult to compare in general, but implementation In Example 1, compared with Comparative Examples 1 and 2, the total processing time is shortened to about 1/4. Therefore, the present invention is expected to be a decontamination method that is more efficient and reliable than conventional methods.
［実施例２］
本実施例による放射性物質除染方法を図２に示す。図２に示す除染方法は、実施例１とは、粉砕工程Ｓ２において粉砕条件だけでなく、新たに酸化剤を添加した点で異なる。さらに、分離回収工程Ｓ５において、篩による最小粒径１００μｍを超える粒子の除去工程を追加した点でも異なる。また、実施例１よりも処理する土壌量を増やし、処理規模を拡大したものである。
[Example 2]
The radioactive substance decontamination method by a present Example is shown in FIG. The decontamination method shown in FIG. 2 differs from Example 1 not only in the grinding conditions in the grinding step S2, but also in that an oxidizing agent is newly added. Furthermore, in the separation and recovery step S5, it is different in that a step of removing particles exceeding a minimum particle size of 100 μm by a sieve is added. Further, the amount of soil to be treated is increased from that in Example 1, and the treatment scale is expanded.
１３７Ｃｓを含む土壌の４０００ｇを、図２に示す密閉式のドラム形状を有する粉砕機１に入れる。粉砕機１には、粒径が２ｃｍの陶器製ボールミルが約１０００個混入されている。土壌体積とボールミル体積との比率は、２：１である。続いて、酸化剤として濃度が３質量％の塩素酸水溶液を３，０００ｃｃ加える。粉砕は、撹拌回転数は６０ｒｐｍで行い、土壌の平均粒径Ｄ５０が１００μｍ以下になるまで、６０〜７０℃で２時間連続的に行った（図２の（ａ））。粉砕後の土壌の平均粒径Ｄ５０は、粉砕前の土壌の平均粒径と比べると１／３以下に微粉砕されていることが分かった。実施例１と同じように、放射線量は、Ｇｅ半導体検出器（ＣＡＮＢＥＲＡ製）を使用し、計数値（Ｃｔｓ／ｓｅｃ／ｇ）からＢｑ／ｋｇに換算した。また、平均粒径Ｄ５０は、ＪＩＳ Ａ １２０４規格に基づいてふるい分析によって得られる粒径加積曲線から求めた。 4000 g of soil containing 137 Cs is put into a crusher 1 having a sealed drum shape shown in FIG. In the pulverizer 1, about 1000 ceramic ball mills having a particle diameter of 2 cm are mixed. The ratio of soil volume to ball mill volume is 2: 1. Subsequently, 3,000 cc of an aqueous chloric acid solution having a concentration of 3% by mass is added as an oxidizing agent. Milling, agitation rotational speed is carried out at 60 rpm, until the average particle diameter D 50 of the soil is 100μm or less, was performed 2 hours continuously at 60 to 70 ° C. (in FIG. 2 (a)). The average particle diameter D 50 of the soil after grinding, was found to be finely pulverized to less than 1/3 compared with the average particle size of the soil before pulverization. As in Example 1, the radiation dose was converted from a count value (Cts / sec / g) to Bq / kg using a Ge semiconductor detector (manufactured by CANBERA). The average particle diameter D 50 was determined from the grain size accumulation curve obtained by sieve analysis based on JIS A 1204 standard.
次いで、粉砕後の土壌２を水洗用容器３にいれた後、１５，０００ｍｌの水を注入して１０分間浸漬することによって洗浄を行った（図２の（ｂ））。その後、呼び寸法が１００μｍである金属製篩を用いて、最大粒径１００μｍを超える粒子の選別及び分別を行った（図２の（ｃ））。選別及び分別後の土壌は、洗浄水を含んだままの状態で孔径が１μｍのろ紙を用いて濾過し（図２の（ｄ））、さらに乾燥を行った。濾過水溶液は、１３７Ｃｓ精製凝集用容器４を用いて、１３７Ｃｓの精製凝集を行う（図２の（ｅ））．
Next, after the
濾過及び乾燥後、ろ紙上の残渣として得られる残土の放射線量を、粉砕前の初期の土壌のものと比べると、放射線量の単位質量当たりの減衰率は約５０％であった。このように、本実施例は、実施例１と対比すると、除染効果が高くなることが確認できた。除染効果の向上は、粉砕条件の変更により土壌の微粉砕が均一に進んだこと、粉砕時に酸化剤を添加したことによる顆粒状放射性物質の表面酸化の促進、及び最小粒径１００μｍを超える粒子の除去によって効率的な分離回収が行われたこと等の効果が相乗的に働いたためと考えられる。 When the radiation dose of the residual soil obtained as a residue on the filter paper after filtration and drying was compared with that of the initial soil before pulverization, the attenuation rate per unit mass of the radiation dose was about 50%. Thus, it was confirmed that the present example has a higher decontamination effect as compared with Example 1. Improvement of decontamination effect is due to the fact that the fine pulverization of the soil has progressed uniformly by changing the pulverizing conditions, the surface oxidation of the granular radioactive material is promoted by adding an oxidizing agent at the time of pulverization, and particles exceeding the minimum particle size of 100 μm This is considered to be due to synergistic effects such as efficient separation / recovery performed by the removal.
さらに、図２に示す放射性物質除染方法において、粉砕後の土壌から最小粒径１ｍｍを超える粗粒子を選別する選別工程Ｓ２を追加する場合には、濾過及び乾燥後に、ろ紙上の残渣として得られる残土は放射線量の単位質量当たりの減衰率が５０％を超え、選別工程Ｓ２を追加しない場合よりも除染効果がやや向上することが確認された。 Furthermore, in the radioactive substance decontamination method shown in FIG. 2, when adding a sorting step S2 for selecting coarse particles having a minimum particle size of 1 mm from the ground soil after pulverization, it is obtained as a residue on the filter paper after filtration and drying. It was confirmed that the residual soil produced had a radiation dose attenuation rate of more than 50%, and the decontamination effect was slightly improved as compared with the case where the sorting step S2 was not added.
実施例１−２においては汚染土壌の除染方法についての実験結果を示しているが、本発明の除染方法は汚染焼却灰に対しても適用することができる。特に、焼却灰は、放射性物質の凝集が顕著であり高い放射線量を示すだけでなく、水蒸気又は保管時や貯蔵時の圧力等によって顆粒状になって存在する確率が高いため、本発明の除染方法によってより高い除染効果を得ることが期待できる。 Although the experimental result about the decontamination method of contaminated soil is shown in Example 1-2, the decontamination method of this invention is applicable also to contaminated incineration ash. In particular, incinerated ash not only exhibits a high agglomeration of radioactive substances and shows a high radiation dose, but also has a high probability of being present in the form of granules due to water vapor or pressure during storage or storage. A higher decontamination effect can be expected by the dyeing method.
以上のように、本発明によれば、セシウム等の放射性物質で汚染された土壌又は焼却灰を初期の大きさよりも小さく粉砕して表面積を増やすことによって、前記放射性物質が酸化されやすい環境が創出され、水洗等の簡便な方法を使って効率的で、且つ確実な除染を行うことができる。さらに、粉砕工程を酸化剤の存在下で行うことによって放射性物質の酸化が促進されるため、除染効果の一層の向上が図れる。それによって、放射性物質で汚染された土壌又は焼却灰の除染が短時間で十分に行えるため、環境への悪影響を低減し、安全性を高めることができる。加えて、汚染土壌又は汚染焼却灰の再生及び再利用を促進できることから、その有用性は極めて高い。 As described above, according to the present invention, the soil or incinerated ash contaminated with radioactive substances such as cesium is pulverized smaller than the initial size to increase the surface area, thereby creating an environment in which the radioactive substances are easily oxidized. In addition, efficient and reliable decontamination can be performed using a simple method such as washing with water. Furthermore, since the oxidation of the radioactive substance is promoted by performing the pulverization step in the presence of an oxidizing agent, the decontamination effect can be further improved. Thereby, decontamination of soil contaminated with radioactive substances or incinerated ash can be sufficiently performed in a short time, and thus adverse effects on the environment can be reduced and safety can be enhanced. In addition, since the regeneration and reuse of contaminated soil or contaminated incineration ash can be promoted, its usefulness is extremely high.
１・・・粉砕機、２・・・粉砕後の土壌、３・・・水洗用容器、４・・・１３７Ｃｓ精製凝集用容器。 DESCRIPTION OF SYMBOLS 1 ... Crusher, 2 ... Soil after grinding | pulverization, 3 ... Container for water washing, 4 ... 137 Container for Cs refinement | aggregation.
Claims (10)
前記放射性物物質で汚染された土壌又は焼却灰を回収又は捕集する工程と、該回収又は捕集する工程後の土壌又は焼却灰を室温又は加温下で機械的に粉砕後の平均粒径が１ｍｍ以下となるまで粉砕する粉砕工程と、該粉砕工程後の土壌又は焼却灰を水洗する水洗工程と、該水洗工程後の土壌又は焼却灰から前記放射性物質を含有する水を分離して回収する分離回収工程とを有することを特徴とする汚染土壌又は汚染焼却灰の除染方法。 A decontamination method for soil or incinerated ash contaminated with radioactive material,
The step of recovering or collecting soil or incinerated ash contaminated with the radioactive material, and the average particle size after mechanically pulverizing the soil or incinerated ash after the step of recovering or collecting at room temperature or under heating Pulverizing process until the water becomes 1 mm or less , water washing process for washing the soil or incinerated ash after the pulverizing process, and separating and collecting the water containing the radioactive substance from the soil or incinerated ash after the water washing process A decontamination method for contaminated soil or contaminated incineration ash, comprising
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