JP5766028B2 - Radiocesium adsorption method - Google Patents
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本発明は、溶存するオゾン濃度が０．０１〜５ｍｇ／Ｌの水中で少なくとも２カ月間液相酸化された活性炭を用いて流体中の放射性セシウムを吸着する方法に関する。 The present invention relates to a method of adsorbing radioactive cesium in a fluid using activated carbon that has been subjected to liquid phase oxidation for at least 2 months in water having a dissolved ozone concentration of 0.01 to 5 mg / L.
原子力発電所の事故などに伴って、放射性セシウム１３４、放射性セシウム１３７などが大気中や水中に漏出し環境汚染を引き起こす。放射性セシウム１３４、放射性セシウム１３７の半減期は放射性ヨウ素１３１の半減期である約８日に比べて約３０年以上と非常に長く、長期間にわたって環境汚染を引き起こし、人体に対する被爆が続くために、流体中のこれら放射性セシウムを効率よく除去する方法の出現が強く望まれている。 In association with an accident at a nuclear power plant, radioactive cesium 134, radioactive cesium 137, etc. leak into the atmosphere or water, causing environmental pollution. The half-life of radioactive cesium 134 and radioactive cesium 137 is very long, about 30 years or more compared to about 8 days, which is the half-life of radioactive iodine 131, causing environmental pollution over a long period of time. The emergence of a method for efficiently removing these radioactive cesiums in fluids is strongly desired.
放射性セシウムの吸着剤としては、天然ゼオライト、イオン交換樹脂が知られており、活性炭は、放射性セシウムをほとんど吸着しないと言われている (非特許文献１) 。
従来、放射性セシウムを吸着・除去する方法として、たとえば、硝酸水溶液中の放射性セシウムを不溶性フェロシアン化物吸着剤で吸着する方法（特許文献１）、ゼオライトイオン交換法で放射性セシウムを除去する方法（特許文献２）などが知られている。これら先行技術は、前処理工程が複雑であり、放射性セシウム除去効率が悪く、かつ、吸着容量が小さいためにこれらの吸着剤を頻繁に交換しなければならず、被爆されやすい多くの作業を伴いない実用上問題が多かった。
また、酸化処理した繊維状活性炭を放射性核種吸着材として利用すること（特許文献３）も知られている。この特許文献によれば、繊維状活性炭を酸化する方法として、３００〜７００℃の温度で１０分間〜５時間の空気酸化、１００〜５００ｐｐｍの気相オゾン酸化、過酸化水素による液相酸化などが開示されているが、このような過酷な条件で酸化された繊維状活性炭では、放射性セシウムの吸着速度が遅く、また放射性セシウムの吸着容量に限界があるために満足できる吸着材ではない。
本発明者は、平成１８年５月頃からオゾン・活性炭法の高度浄水処理場で行なわれている活性炭に対する液相オゾン酸化現象を追跡調査するために、実験室で模擬的なテストを長期間かけて実施し、溶存するオゾンが約１ｍｇ／Ｌの極低濃度で酸化された活性炭をいろいろな角度から分析、検討した。その研究の一部を全国水道研究発表会で発表した。（非特許文献２）
As a radioactive cesium adsorbent, natural zeolite and ion exchange resin are known, and activated carbon is said to hardly adsorb radioactive cesium (Non-patent Document 1).
Conventionally, as a method for adsorbing and removing radioactive cesium, for example, a method of adsorbing radioactive cesium in an aqueous nitric acid solution with an insoluble ferrocyanide adsorbent (Patent Document 1), a method of removing radioactive cesium by a zeolite ion exchange method (patent) Document 2) is known. In these prior arts, the pretreatment process is complicated, the radioactive cesium removal efficiency is poor, and the adsorption capacity is small, so these adsorbents must be replaced frequently, and many operations are easily exposed. There were not many practical problems.
It is also known to use oxidized activated fibrous activated carbon as a radionuclide adsorbent (Patent Document 3). According to this patent document, as a method for oxidizing fibrous activated carbon, air oxidation at a temperature of 300 to 700 ° C. for 10 minutes to 5 hours, gas phase ozone oxidation at 100 to 500 ppm, liquid phase oxidation with hydrogen peroxide, etc. Although it is disclosed, fibrous activated carbon oxidized under such severe conditions is not a satisfactory adsorbent because the adsorption rate of radioactive cesium is slow and the adsorption capacity of radioactive cesium is limited.
In order to follow up the liquid-phase ozone oxidation phenomenon for activated carbon that has been carried out at the advanced water treatment plant using the ozone / activated carbon method from around May 2006, the present inventor has conducted a long-term simulation test in the laboratory. The activated carbon in which dissolved ozone was oxidized at an extremely low concentration of about 1 mg / L was analyzed and examined from various angles. Part of the research was presented at the National Waterworks Research Presentation. (Non-Patent Document 2)
本発明は、流体中の放射性セシウムを簡単な操作で効率よく吸着する方法を提供することを目的としている。 An object of the present invention is to provide a method for efficiently adsorbing radioactive cesium in a fluid by a simple operation.
本発明者は、前記の点などを鑑み鋭意研究した結果、極低濃度のオゾンが溶存した水中で長期間かけて非常にゆっくり液相酸化した活性炭が、流体中の放射性セシウムを効率よく吸着することを見出した。このように長時間かけて緩やかに酸化された活性炭は、短時間に過酷な条件で酸化された活性炭に比べて、不活性ガス気流中において２５０℃まで加熱した際に発生する炭酸ガス量が非常に多く、放射性セシウムを極めてよく吸着することを見出した。これらの知見を基にさらに研究を重ねた結果、本発明を完成した。
すなわち本発明は、
（１）溶存するオゾン濃度が０．０１〜５ｍｇ／Ｌの水中で少なくとも２カ月間液相オゾン酸化された活性炭を放射性セシウムまたはその化合物を含有する流体と接触させることを特徴とする流体中の放射性セシウムまたはその化合物の吸着方法、
（２）溶存するオゾン濃度が０．０１〜５ｍｇ／Ｌの水中で少なくとも２カ月間液相オゾン酸化された活性炭が少なくとも２カ月間オゾン・活性炭法高度浄水処理により液相オゾン酸化された活性炭である（１）に記載の放射性セシウムまたはその化合物の吸着方法、
である。
As a result of diligent research in view of the above points, the present inventor efficiently adsorbs radioactive cesium in a fluid by activated carbon that has been subjected to liquid phase oxidation very slowly over a long period of time in water in which extremely low concentration of ozone is dissolved. I found out. In this way, activated carbon that has been gently oxidized over a long period of time has a significantly higher amount of carbon dioxide gas when heated to 250 ° C. in an inert gas stream than activated carbon that has been oxidized under severe conditions in a short time. It was found that it adsorbs radioactive cesium very well. As a result of further research based on these findings, the present invention was completed.
That is, the present invention
(1) In a fluid characterized by contacting activated carbon that has been subjected to liquid phase ozone oxidation in water having a dissolved ozone concentration of 0.01 to 5 mg / L for at least 2 months with a fluid containing radioactive cesium or a compound thereof. Method for adsorbing radioactive cesium or a compound thereof,
(2) Activated carbon that has been subjected to liquid phase ozone oxidation for at least 2 months in water having a dissolved ozone concentration of 0.01 to 5 mg / L for at least 2 months by liquid phase ozone oxidation by ozone / activated carbon method advanced water purification treatment. A method of adsorbing radioactive cesium or a compound thereof according to (1),
It is.
本発明で使用される吸着剤は、木炭、コークス、石炭、ヤシ殻、樹脂、石油残渣などを原料として通常の方法により賦活され、その形状は、粉末状、破砕状、円柱状、球状、ハニカム状、繊維状などいかなるものでもよい。これらの活性炭を、溶存するオゾン濃度が０．０１〜５ｍｇ／Ｌ、好ましくは０．０５〜２ｍｇ／Ｌ、より好ましくは０．１〜１ｍｇ／Ｌの極低濃度である水中で少なくとも２カ月間、好ましくは１〜６年間に亘り非常にゆっくり液相酸化したもので、比表面積は、５０ｍ２／ｇ以上、好ましくは１００〜２５００ｍ２／ｇのものが本発明で用いられる吸着剤である。 The adsorbent used in the present invention is activated by a normal method using charcoal, coke, coal, coconut husk, resin, petroleum residue, etc. as a raw material, and its shape is powder, crushed, columnar, spherical, honeycomb Any shape such as a shape or a fiber shape may be used. These activated carbons have a dissolved ozone concentration of 0.01 to 5 mg / L, preferably 0.05 to 2 mg / L, more preferably 0.1 to 1 mg / L in water at a very low concentration for at least 2 months. preferably obtained by very oxidized slowly liquid phase over 1-6 years, specific surface area, 50 m 2 / g or more, adsorbent used preferably in the present invention include the 100~2500m 2 / g.
一般に活性炭を酸化する方法として、高温下に酸素含有ガス(空気)で酸化する方法、気相でオゾン酸化する方法、過酸化水素水で液相酸化する方法などがよく知られている。このような方法による酸化では、比較的に短時間に酸化された活性炭を得ることができるが、この場合活性炭が過度の酸化を受けるために、酸化過程で炭酸ガスが激しく発生し、活性炭のガス化（活性炭の重量減少）を伴う。このような過度に酸化処理された活性炭には、放射性セシウムを吸着する活性点（表面酸化物）が酸化過程で大部分失われ、放射性セシウムの吸着性能に限界があることが判明した。 In general, as a method of oxidizing activated carbon, a method of oxidizing with an oxygen-containing gas (air) at a high temperature, a method of oxidizing with ozone in the gas phase, a method of oxidizing with liquid hydrogen with aqueous hydrogen peroxide and the like are well known. In the oxidation by such a method, activated carbon that has been oxidized in a relatively short time can be obtained. In this case, the activated carbon is excessively oxidized, so that carbon dioxide gas is generated vigorously during the oxidation process. Accompanied by a decrease in the weight of activated carbon. It has been found that the active sites (surface oxides) that adsorb radioactive cesium are mostly lost during the oxidation process in such excessively oxidized activated carbon, and the adsorption performance of radioactive cesium is limited.
これに対して、溶存するオゾンが０．０１〜５ｍｇ／Ｌの極低濃度である水中で、活性炭を非常にゆっくり酸化すると、酸化過程で炭酸ガスの発生が非常に少なく、したがって、酸化後の活性炭の表面には放射性セシウムを吸着する有効な活性点（表面酸化物）が多量に温存され、効率よく放射性セシウムを吸着することを見出した。
すなわち本発明者は、前述の第５９回全国水道研究発表会で発表したように溶存するオゾン濃度が１ｍｇ／Ｌである水中で各種活性炭を最長１２０日間液相酸化した。その結果、いずれの場合も活性炭が緩慢に液相酸化されるためにこの反応中に活性炭の重量および表面酸化物がいずれも増加し続けた。
溶存するオゾン濃度が０．０１〜５ｍｇ／Ｌという極低濃度オゾンで活性炭を非常に緩やかに液相酸化すると、酸化に伴う炭酸ガスの発生が非常に少なく、活性炭の表面に多量の酸化物が生成し、活性炭の重量は逆に増加することは、明白な事実である。このような緩慢な酸化条件下で活性炭を液相オゾン酸化することによって、活性炭の表面には放射性セシウムを吸着する有効な活性点（表面酸化物）が多量に温存され、放射性セシウムの吸着性能が飛躍的に向上することを新たに見出したのである。
On the other hand, when activated carbon is oxidized very slowly in water in which dissolved ozone is a very low concentration of 0.01 to 5 mg / L, the generation of carbon dioxide gas is very small during the oxidation process. It was found that a large amount of effective active sites (surface oxides) that adsorb radioactive cesium were preserved on the surface of the activated carbon, and the radioactive cesium was adsorbed efficiently.
That is, the present inventor liquid-phase oxidized various activated carbons in water having a dissolved ozone concentration of 1 mg / L for up to 120 days as announced at the 59th National Waterworks Research Conference. As a result, the weight of activated carbon and the surface oxide both continued to increase during this reaction due to the slow liquid phase oxidation of the activated carbon in each case.
When activated carbon is very slowly liquid-phase oxidized with an extremely low concentration of ozone of 0.01 to 5 mg / L, the amount of carbon dioxide that accompanies the oxidation is very small, and a large amount of oxide is present on the surface of the activated carbon. It is a clear fact that the weight of the activated carbon that is produced increases on the contrary. By liquid-phase ozone oxidation of activated carbon under such slow oxidation conditions, a large amount of effective active sites (surface oxides) that adsorb radioactive cesium are preserved on the surface of activated carbon, and the adsorption performance of radioactive cesium is improved. It was newly found that it can be improved dramatically.
活性炭に対する「比較的に短時間おける激しい酸化または過酷な酸化」と「長時間かける緩やかな極低濃度オゾンでの液相酸化」との間には、明らかな差異が生じる。そのためにいろいろな酸化方法で処理した活性炭を窒素気流中で２５０℃まで加熱し、その際に酸化活性炭試料から発生する炭酸ガス量を水酸化バリウム水溶液に吸収させて、炭酸バリウムとして沈澱させる方法で定量したところ、酸化活性炭試料からの炭酸ガス発生量（ｍｇ／ｇ）と酸化活性炭試料の放射性セシウム吸着性能（ｍｇ／ｇ）との間に密接な相関関係があることを見出した。 There is a clear difference between “violent or severe oxidation over a relatively short period of time” and “liquid phase oxidation with slow, very low concentration ozone over a long period of time” for activated carbon. For this purpose, activated carbon treated by various oxidation methods is heated to 250 ° C. in a nitrogen stream, and the amount of carbon dioxide gas generated from the oxidized activated carbon sample is absorbed by the barium hydroxide aqueous solution and precipitated as barium carbonate. As a result of quantification, it was found that there is a close correlation between the amount of carbon dioxide gas generated from the oxidized activated carbon sample (mg / g) and the radioactive cesium adsorption performance (mg / g) of the oxidized activated carbon sample.
引用の特許文献３における活性炭の酸化法と本発明おける酸化法とを８〜３２メッシュの瀝青炭系活性炭Ａ（ＢＥＴ比表面積１１５０ｍ２／ｇ）およびヤシ殻系活性炭Ｂ（ＢＥＴ比表面積１２５０ｍ２／ｇ）について実施した。
すなわち、
１．引用の特許文献３に基づく酸化法
（１）約１８０ｐｐｍオゾンで１５日間気相酸化したもの、
（２）２５０〜６００℃で２０分間酸素酸化したもの、
（３）５重量％過酸化水素で８０℃３０分間液相酸化したもの
２．本発明に基づく酸化法
（１）水中の濃度オゾン約１．０ｍｇ／Ｌで４０日間〜１２０日間液相酸化したもの、
（２）オゾン・活性炭法高度浄水処理で約３年間行われた液相オゾン（濃度約０．２６ｍｇ／Ｌ）酸化したもの、
のそれぞれについて分析、検討を行った。
これらの酸化処理の実験については、比較例１〜３および実施例１、２で詳しく述べる。
The activated carbon oxidation method in the cited Patent Document 3 and the oxidation method in the present invention are 8 to 32 mesh bituminous coal activated carbon A (BET specific surface area 1150 m 2 / g) and coconut shell activated carbon B (BET specific surface area 1250 m 2 / g). ).
That is,
1. Oxidation method based on cited Patent Document 3 (1) Gas phase oxidation with about 180 ppm ozone for 15 days,
(2) Oxygen-oxidized at 250 to 600 ° C. for 20 minutes,
(3) Liquid phase oxidation with 5 wt% hydrogen peroxide at 80 ° C. for 30 minutes Oxidation method based on the present invention (1) Liquid phase oxidation with ozone concentration of about 1.0 mg / L in water for 40 days to 120 days,
(2) Ozone / activated carbon method Liquid phase ozone (concentration of about 0.26 mg / L) oxidized for about 3 years by advanced water purification treatment,
Each was analyzed and examined.
These oxidation treatment experiments will be described in detail in Comparative Examples 1 to 3 and Examples 1 and 2.
東京都をはじめ大都市の浄水場では、取水の品質の悪化に伴い、１９９２年頃から、オゾン・活性炭法による高度浄水処理、すなわち、たとえば、［凝集沈殿→砂濾過→オゾン処理→粒状活性炭処理→後塩素注入］という処理フローで高度浄水処理が行われている。これらの浄水場では、前処理された水はオゾン接触池において１００００ｐｐｍ以上のオゾンを含有する酸素ガスで接触酸化され、水中の有機化合物などを酸化分解した後、濃度０．１〜１．０ｍｇ／Ｌの溶存オゾン水を後置の粒状活性炭層に接触させる。この活性炭層での溶存オゾン水の接触時間は、通常５〜２０分（空間速度３〜１２Ｌ／Ｌ／時）である。このような高度浄水処理場での活性炭に対するオゾン負荷量は、1日当たり０．０２〜０．５０ｍｇ／ｇ−活性炭であり、極低オゾン負荷量で長期間（１〜６年間）かけて活性炭が非常にゆっくりと液相酸化される。すなわち、このような極低濃度オゾンで長期間かけて非常にゆっくり液相酸化された活性炭は、２５０℃までの加熱に際して炭酸ガスが極めて多量生成することを見出した。したがって、オゾン・活性炭法による高度浄水処理場で少なくとも２ヶ月間、極低濃度オゾンで液相酸化された活性炭は流体中の放射性セシウムを非常に効果的に吸着することを確認した。 In water treatment plants in Tokyo and other large cities, with the deterioration of water intake quality, from around 1992, advanced water treatment by the ozone / active carbon method, for example, [coagulation precipitation → sand filtration → ozone treatment → granular activated carbon treatment → Advanced water purification treatment is performed with a treatment flow of “post-chlorine injection”. In these water purification plants, the pretreated water is contact-oxidized with oxygen gas containing 10000 ppm or more of ozone in an ozone contact pond, and oxidatively decomposes organic compounds in water. L dissolved ozone water is brought into contact with the granular activated carbon layer afterwards. The contact time of dissolved ozone water in this activated carbon layer is usually 5 to 20 minutes (space velocity 3 to 12 L / L / hour). Ozone load for activated carbon with such advanced water treatment plants, daily 0.02~0.50mg / g - a charcoal, a long period of time at very low ozone load (1-6 year) over activated carbon Liquid phase oxidation very slowly. That is, it has been found that such activated carbon that has been subjected to liquid phase oxidation very slowly over a long period of time with extremely low concentration ozone produces a very large amount of carbon dioxide when heated to 250 ° C. Therefore, it was confirmed that activated carbon that was liquid-phase oxidized with ultra-low concentration ozone for at least two months in an advanced water treatment plant using the ozone / active carbon method adsorbs radioactive cesium in the fluid very effectively.
日本全国でオゾン・活性炭法による高度浄水処理場は多数稼働しており、これらの高度浄水処理場から毎年数千〜数万トンのオゾン液相酸化活性炭が排出されている。このオゾン液相酸化活性炭はそのままの状態で放射性セシウムを非常によく吸着するので、オゾン液相酸化活性炭を特に製造する必要がなく、排出されたそのままの状態で放射性セシウム吸着剤として利用できることは本発明の最大の特長である。
特に原子力発電所の事故時などでは、緊急的に放射性セシウムを吸着・除去するために多量の放射性セシウム吸着剤が必要となるので、高度浄水処理場から排出される極低濃度オゾン液相酸化活性炭が放射性セシウム吸着剤として代用できることは、漏洩した放射性セシウムによる環境汚染および人体への被爆防止などの点で意義が大きい。
Many advanced water treatment plants using the ozone / activated carbon method are in operation throughout Japan, and thousands of tens of thousands of tons of ozone liquid phase oxidized activated carbon are discharged from these advanced water treatment plants every year. This ozone liquid phase oxidized activated carbon adsorbs radioactive cesium very well as it is, so it is not necessary to produce ozone liquid phase oxidized activated carbon and it can be used as a radioactive cesium adsorbent as it is discharged. This is the greatest feature of the invention.
Particularly in the event of an accident at a nuclear power plant, a large amount of radioactive cesium adsorbent is necessary to urgently adsorb and remove radioactive cesium, so extremely low concentration ozone liquid phase oxidized activated carbon discharged from advanced water treatment plants That can be substituted as a radioactive cesium adsorbent is significant in terms of environmental pollution caused by leaked radioactive cesium and prevention of exposure to human bodies.
さらに、本発明においては、上記のようにして得られた極低濃度オゾン液相酸化活性炭（本発明の吸着剤）に放射性セシウムを含む流体を通常の方法で接触させることによって、流体中の放射性セシウムを効率よく吸着することができる。たとえば、本発明の吸着剤を充填した装置に放射性セシウムを含む流体を流通する方法などが考えられる。また、ガスマスクの充填剤として本発明の吸着剤を使用する方法や、空気清浄機のフィルターとして本発明の吸着剤を利用する方法、放射性セシウムを含む水が入った容器内に本発明の吸着剤を存在させて放射性セシウムを吸着する方法など、通常、よく行なわれている方法などが考えられる。
本発明の吸着剤を気相で使用する場合、セシウム吸着性能に対する温度、湿度の影響が小さいのも本発明の他の大きな特徴の一つである。すなわち、温度が１２０℃以下であれば、相対湿度７５％以上でも良好な放射性セシウムの吸着性能を維持する。
Further, in the present invention, the radioactive material in the fluid is brought into contact with the ultra-low concentration ozone liquid phase oxidized activated carbon (the adsorbent of the present invention) obtained as described above by contacting the fluid containing radioactive cesium by an ordinary method. Cesium can be adsorbed efficiently. For example, a method of circulating a fluid containing radioactive cesium in an apparatus filled with the adsorbent of the present invention can be considered. Further, the method of using the adsorbent of the present invention as a gas mask filler, the method of using the adsorbent of the present invention as a filter of an air cleaner, the adsorption of the present invention in a container containing water containing radioactive cesium. Usually used methods such as a method of adsorbing radioactive cesium in the presence of an agent can be considered.
When the adsorbent of the present invention is used in a gas phase, one of the other major characteristics of the present invention is that the influence of temperature and humidity on the cesium adsorption performance is small. That is, when the temperature is 120 ° C. or lower, good radiocesium adsorption performance is maintained even at a relative humidity of 75% or higher.
本発明に使用される活性炭は、溶存するオゾン濃度が０．０１〜５ｍｇ／Ｌの水中で少なくとも２カ月間液相酸化されたもので、その表面に放射性セシウムを選択的に、かつ、効率よく吸着する活性点・表面酸化物（２５０℃までの加熱に伴う炭酸ガス量）を多量に有するもので、ＢＥＴ比表面積が大きく、かつ、耐薬品性に優れており、かつ、流体中に共存する成分（水蒸気などを含む）の影響を受けにくく、流体中の放射性セシウムを効率よく吸着できる。特に、オゾン・活性炭法による高度浄水場では、水中のオゾン濃度０．１〜１ｍｇ／Ｌで少なくとも１年以上の期間液相酸化され、このようにして得られる活性炭は、放射性セシウムを吸着する方法に最適である。 The activated carbon used in the present invention has been subjected to liquid phase oxidation for at least 2 months in water having a dissolved ozone concentration of 0.01 to 5 mg / L, and selectively and efficiently adds radioactive cesium to the surface thereof. It has a large amount of active sites and surface oxides to adsorb (the amount of carbon dioxide that accompanies heating up to 250 ° C), has a large BET specific surface area, excellent chemical resistance, and coexists in the fluid. It is difficult to be affected by components (including water vapor) and can efficiently adsorb radioactive cesium in the fluid. In particular, in an advanced water purification plant using the ozone / active carbon method, liquid phase oxidation is performed at a ozone concentration of 0.1 to 1 mg / L in water for a period of at least one year, and the activated carbon thus obtained adsorbs radioactive cesium. Ideal for.
以下に実施例をあげて、本発明を具体的に説明する。実施例では、便宜上、放射性セシウム化合物の代わりに非放射性のＣｓ５５の化合物を使用し、模擬液および模擬ガスで実験した。これら模擬液および模擬ガスでの実験においても、両者は化学的には全く同じ性質を有し、Ｃｓ５５を用いた実験でも放射性セシウム化合物を用いた結果と同じである。
［比較例１］
The present invention will be specifically described with reference to the following examples. In the examples, for the sake of convenience, a non-radioactive Cs55 compound was used in place of the radioactive cesium compound, and experiments were performed with a simulated liquid and a simulated gas. In the experiments with the simulated liquid and the simulated gas, both have the same chemical properties, and the experiment using Cs55 is the same as the result using the radioactive cesium compound.
[Comparative Example 1]
気相オゾン酸化：特許文献３に基づく酸化法（１）
内径９４ｍｍφのアクリル製カラムに８〜３２メッシュの瀝青炭系活性炭Ａ（ＢＥＴ比表面積１１５０ｍ２／ｇ）および８〜３２メッシュのヤシ殻系活性炭Ｂ（ＢＥＴ比表面積１２５０ｍ２／ｇ）の各４００ｍLの充填層を形成して、下部からオゾン約１８０ｐｐｍ含有空気を流量５L／分で吹き込み、各活性炭を気相でオゾン酸化した。オゾン酸化時間は、いずれも１５日間であった。活性炭Ａおよび活性炭Ｂとこれらの気相オゾン酸化活性炭試料のａ1およびｂ１につい
て、次の方法で２５０℃加熱に伴う「炭酸ガス発生量」および「放射性セシウムの吸着性能」を測定した。これらの測定結果は、表１の通りであった。
Gas phase ozone oxidation: oxidation method based on Patent Document 3 (1)
An acrylic column with an inner diameter of 94 mmφ is packed with 400 mL each of 8-32 mesh bituminous coal-based activated carbon A (BET specific surface area 1150 m 2 / g) and 8-32 mesh coconut shell-based activated carbon B (BET specific surface area 1250 m 2 / g). A layer was formed, and air containing about 180 ppm of ozone was blown from the bottom at a flow rate of 5 L / min, and each activated carbon was subjected to ozone oxidation in the gas phase. The ozone oxidation time was 15 days for all. With respect to activated carbon A and activated carbon B and a1 and b1 of these vapor-phase ozone-oxidized activated carbon samples, “carbon dioxide generation amount” and “adsorption performance of radioactive cesium” accompanying heating at 250 ° C. were measured by the following methods. These measurement results are shown in Table 1.
炭酸ガス発生量の測定法
内径１０ｍｍφ×長さ１０００ｍｍの石英カラムに活性炭試料５００ｍｇを入れ、試料の前後は十分に乾燥させた石英ガラスウールに固定し、電気環状炉にセットした。また石英カラム両端をゴム栓で蓋をしてゴム栓には窒素を導入および排出するための孔をあける。５０ｍｌ／分の流速で窒素を石英カラムに流しながら、１００℃まで加熱昇温し、次いで、出口ガスを１０ｍ-ｍｏｌ／Ｌ水酸化バリウム水溶液１００ｍＬを入れた吸収瓶に接続し、１００℃／時間の昇温速度で２５０℃まで加熱昇温した。２５０℃になってから、さらに１０分間２５０℃で保持し、発生した炭酸ガスを水酸化バリウム水溶液に吸収させ、炭酸バリウムとして沈澱させ、上済み液をサンプリングして塩酸で中和滴定して、残留水酸化バリウム量から発生炭酸ガス量（ｍｇ／ｇ）を求める。
Measurement method of carbon dioxide generation amount 500 mg of the activated carbon sample was put in a quartz column having an inner diameter of 10 mmφ × 1000 mm in length, and the sample was fixed on quartz glass wool that had been sufficiently dried and set in an electric annular furnace. Also, both ends of the quartz column are covered with rubber stoppers, and holes for introducing and discharging nitrogen are made in the rubber stoppers. While flowing nitrogen through the quartz column at a flow rate of 50 ml / min, the temperature was raised to 100 ° C., and then the outlet gas was connected to an absorption bottle containing 100 mL of a 10 m-mol / L barium hydroxide aqueous solution. The temperature was raised to 250 ° C. After reaching 250 ° C., hold at 250 ° C. for another 10 minutes, absorb the generated carbon dioxide gas in an aqueous barium hydroxide solution, precipitate it as barium carbonate, sample the supernatant and neutralize and titrate with hydrochloric acid, The amount of generated carbon dioxide (mg / g) is determined from the amount of residual barium hydroxide.
セシウムの吸着性能の測定法
活性炭試料を乳鉢で微粉砕した１００ｍｇをＣｓＯＨ−２５ｍｇ（Ｃｓイオン２２ｍｇ）を含む水溶液１５ｍＬに懸濁させて、２５℃で２時間振とうさせた後、ガラス濾過器で濾過した。濾液５ｍＬ中に残留するＣｓイオンを測定してＣｓの吸着性能（ｍｇ／ｇ）を算出した。
Method of measuring cesium adsorption performance 100 mg of activated carbon sample finely pulverized in a mortar was suspended in 15 mL of an aqueous solution containing CsOH-25 mg (Cs ions 22 mg), shaken at 25 ° C. for 2 hours, and then filtered with a glass filter. Filtered. Cs ions remaining in 5 mL of the filtrate were measured to calculate Cs adsorption performance (mg / g).
［比較例２］
[Comparative Example 2]
酸素酸化：特許文献３に基づく酸化法（２）
比較例１の活性炭Ａの各３０ｇを５５ｍｍφの石英ガラス管に充填して、それぞれ２５０、４００、５００、及び６００℃の各温度でＯ２−１０.０ｖｏｌ％含有のＮ２ガスを線流速５ｃｍ／秒で２０分間流通した後、Ｎ２ガス中で常温まで冷却して、酸化活性炭ａ２、ａ３、ａ４およびａ５を得た。これらの試料について比較例１と同様な方法で、「炭酸ガス発生量」および「放射性セシウムの吸着性能」を測定した結果は、表２の通りであった。すなわち酸素酸化では、処理温度の如何を問わず、Ｃｓ吸着性能はそれほど高くはない。
Oxygen oxidation: oxidation method based on Patent Document 3 (2)
Each 30g of activated carbon A of Comparative Example 1 was filled in a quartz glass tube 55Mmfai, respectively 250,400,500, and O 2 -10.0vol% content of N 2 gas linear flow rate 5cm at each temperature of 600 ° C. After being circulated for 20 minutes at / second, the mixture was cooled to room temperature in N 2 gas to obtain oxidized activated carbons a2, a3, a4 and a5. The results of measuring “carbon dioxide generation amount” and “adsorption performance of radioactive cesium” by the same method as in Comparative Example 1 for these samples are shown in Table 2. That is, in oxygen oxidation, Cs adsorption performance is not so high regardless of the treatment temperature.
過酸化水素水酸化：特許文献３に基づく酸化法（３）
５００ｍＬのビーカーに５重量％の過酸化水素水１００ｍＬを入れ、８０℃の水浴中で８０℃に加熱した。この過酸化水素水に比較例１の活性炭Ａの１０ｇを入れ攪拌しながら３０分間酸化した。酸化後の活性炭をろ過して１００℃で乾燥
した。この酸化処理活性炭試料ａ６について比較例１と同様な方法で、「炭酸ガス発生量」および「放射性セシウムの吸着性能」を測定した結果は、それぞれ１７ｍｇ／ｇおよび３２ｍｇ／ｇであった。
Hydrogen peroxide hydroxylation: oxidation method based on Patent Document 3 (3)
A 500 mL beaker was charged with 100 mL of 5 wt% hydrogen peroxide and heated to 80 ° C in an 80 ° C water bath. In this hydrogen peroxide solution, 10 g of the activated carbon A of Comparative Example 1 was added and oxidized with stirring for 30 minutes. The oxidized activated carbon was filtered and dried at 100 ° C. With respect to this oxidized activated carbon sample a6, the “carbon dioxide generation amount” and “adsorption performance of radioactive cesium” were measured in the same manner as in Comparative Example 1, and the results were 17 mg / g and 32 mg / g, respectively.
極低濃度オゾン液相酸化（その１）：本発明に基づく酸化法（１）
内径９４ｍｍφのアクリル製カラムに比較例１の活性炭Ａと活性炭Ｂの各４００ｍLの充填層を形成して、この上部からオゾン１．０ｍｇ／Ｌ含有の蒸留水を線流速１ｃｍ／分で４０日間、６０日間、８０日間、１００日間および１２０日間流通し、活性炭を極低濃度のオゾンで非常にゆっくり液相酸化し、酸化活性炭試料ａ４０、ａ６０、ａ８０、ａ１００およびａ１２０とｂ４０、ｂ６０、ｂ８０、ｂ１００およびｂ１２０をそれぞれ得た。なお、この実験での活性炭に対するオゾン負荷量は１日当たり約０．４５ｍｇ／ｇ−活性炭に相当する。これらの酸化活性炭試料ａ４０〜ａ１２０とｂ４０〜ｂ１２０について、比較例１と同様な方法で、炭酸ガス発生量および放射性セシウムの吸着性能を測定した結果は、表３のとおりであった。
Extremely low concentration ozone liquid phase oxidation (part 1): oxidation method based on the present invention (1)
A packed bed of 400 mL each of activated carbon A and activated carbon B of Comparative Example 1 was formed on an acrylic column having an inner diameter of 94 mmφ, and distilled water containing 1.0 mg / L of ozone was added from this top for 40 days at a linear flow rate of 1 cm / min. Circulated for 60 days, 80 days, 100 days, and 120 days, and the activated carbon was subjected to liquid phase oxidation very slowly with extremely low concentration ozone, and oxidized activated carbon samples a40, a60, a80, a100 and a120 and b40, b60, b80, b100. And b120 were obtained respectively. In addition, the ozone load with respect to the activated carbon in this experiment is equivalent to about 0.45 mg / g - activated carbon per day. For these oxidized activated carbon samples a40 to a120 and b40 to b120, the amount of carbon dioxide gas generated and the adsorption performance of radioactive cesium were measured in the same manner as in Comparative Example 1, and the results are shown in Table 3.
極低濃度オゾン液相酸化（その２）：本発明に基づく酸化法（２）
比較例１の活性炭Ａをオゾン・活性炭法浄水場で約３年間使用した。この浄水場においては、活性炭の充填層厚さ約２．５ｍ、通水速度約２６０ｍ／日（空間速度約４Ｌ／Ｌ／時）、オゾン濃度約０．２６ｍｇ／Ｌで、活性炭Ａに対するオゾン負荷量は１日当たり約０．０４５ｍｇ／ｇ−活性炭であった。この酸化活性炭試料ａ７について、比較例１と同様な方法で、「炭酸ガス発生量」および「放射性セシウムの吸着性能」を測定した結果は、それぞれ ２８ｍｇ／ｇおよび９０ｍｇ／ｇであった。
以上、比較例１〜３および実施例１〜２の結果から、酸化活性炭各試料に関して「炭酸ガス発生量」と「放射性セシウムの吸着性能」との間には、おおむね良好な相関関係が存在する。すなわち、本発明の実施例１〜２から「炭酸ガス発生量」が２４ｍｇ／ｇ以上の酸化活性炭試料では「放射性セシウムの吸着性能」は、９０ｍｇ／ｇ以上であることがわかる。他方、比較例１〜３の酸化活性炭である対照試料に関する実験結果では、「炭酸ガス発生量」は２０ｍｇ／ｇ以下で「放射性セシウムの吸着性能」は６８ｍｇ／ｇ以下となり、放射性セシウムの吸着性能が著しく劣る。
Extremely low concentration ozone liquid phase oxidation (part 2): oxidation method based on the present invention (2)
The activated carbon A of Comparative Example 1 was used at an ozone / activated carbon method water purification plant for about 3 years. In this water purification plant, the activated carbon packed bed thickness is about 2.5 m, the water flow rate is about 260 m / day (space velocity is about 4 L / L / hour), and the ozone concentration is about 0.26 mg / L. the amount per day to about 0.045 mg / g - was activated carbon. With respect to this oxidized activated carbon sample a7, the “carbon dioxide generation amount” and the “adsorption performance of radioactive cesium” were measured in the same manner as in Comparative Example 1, and the results were 28 mg / g and 90 mg / g, respectively.
As described above, from the results of Comparative Examples 1 to 3 and Examples 1 and 2, there is generally a good correlation between “carbon dioxide generation amount” and “adsorption performance of radioactive cesium” with respect to each sample of the oxidized activated carbon. . That is, it can be seen from Examples 1-2 of the present invention that the “carbon dioxide generation amount” of the oxidized activated carbon sample of 24 mg / g or more has “radioactive cesium adsorption performance” of 90 mg / g or more. On the other hand, in the experimental results on the control sample which is the oxidized activated carbon of Comparative Examples 1 to 3, the “carbon dioxide generation amount” is 20 mg / g or less and the “adsorption performance of radioactive cesium” is 68 mg / g or less, and the adsorption performance of radioactive cesium. Is significantly inferior.
比較例１の活性炭Ａおよび活性炭Ｂ、これらの気相オゾン酸化活性炭試料ａ１およびｂ１、比較例２の酸素酸化活性炭試料ａ２、ａ３、ａ４およびａ５、比較例３の過酸化水素水酸化活性炭試料ａ６、実施例１の極低濃度オゾン液相酸化活性炭ａ１２０およびｂ１２０、さらに実施例２の極低濃度オゾン液相酸化活性炭ａ７について気相流通法による放射性セシウムの吸着実験を行った。
すなわち、上記の各酸化活性炭試料中の含水率を約３０重量％に調整した後、４ｃｍφのカラムに層長が１０ｃｍになるように充填した。このカラムにＣｓＯＨ−０．０１ｍｇ／Ｌ含有の大気（温度２５℃・相対湿度８５％）を３Ｌ／分で流通して、カラムから流出するガス中のＣｓＯＨ濃度を測定して、ＣｓＯＨ破過率が５％になる時間を調べた。その結果を表４に示した。
Activated carbon A and activated carbon B of Comparative Example 1, gas phase ozone oxidized activated carbon samples a1 and b1, oxygen oxidized activated carbon samples a2, a3, a4 and a5 of Comparative Example 2, hydrogen peroxide-oxygenated activated carbon sample a6 of Comparative Example 3 Experiments on the adsorption of radioactive cesium by the vapor-phase flow method were performed on the ultra-low concentration ozone liquid phase oxidized activated carbons a120 and b120 of Example 1 and the extremely low concentration ozone liquid phase oxidized activated carbon a7 of Example 2.
That is, after adjusting the water content in each oxidized activated carbon sample to about 30% by weight, it was packed in a 4 cmφ column so that the layer length was 10 cm. CsOH-0.01 mg / L-containing air (temperature: 25 ° C., relative humidity: 85%) was passed through this column at 3 L / min, and the CsOH concentration in the gas flowing out from the column was measured. The time when 5% was obtained was examined. The results are shown in Table 4.
すなわち、比較的に短時間で過酷な酸化を受けた酸化活性炭試料（対照）では、「炭酸ガス発生量」が、２０ｍｇ／ｇ以下となり、放射性セシウムを吸着する能力が非常に劣る。
これに対して、溶存するオゾン濃度が０．０１〜１ｍｇ／Ｌという極低濃度オゾンで非常に緩やかに液相酸化された酸化活性炭試料（本発明）では、「炭酸ガス発生量」が、２４ｍｇ／ｇ以上となり、放射性セシウムを吸着する能力が飛躍的に向上することが確認された。
That is, in the oxidized activated carbon sample (control) subjected to severe oxidation in a relatively short time, the “carbon dioxide generation amount” is 20 mg / g or less, and the ability to adsorb radioactive cesium is very inferior.
On the other hand, in the oxidized activated carbon sample (invention) that was very gently liquid phase oxidized with an extremely low concentration ozone of 0.01 to 1 mg / L, the “carbon dioxide generation amount” was 24 mg. It was confirmed that the ability to adsorb radioactive cesium dramatically improved.
本発明においては、極低濃度オゾン液相酸化活性炭に放射性セシウムを含む流体を通常の方法で接触させることによって、流体中の放射性セシウムを効率よく吸着することができる。また、ガスマスクの充填剤として本発明の吸着剤を使用する方法や、空気清浄機のフィルターとして本発明の吸着剤を利用する方法、放射性セシウムを含む水が入った容器内に本発明の吸着剤を存在させて放射性セシウムを吸着する方法などがある。 In the present invention, the radioactive cesium in the fluid can be efficiently adsorbed by bringing the fluid containing radioactive cesium into contact with the ultra-low concentration ozone liquid phase oxidized activated carbon by a normal method. Further, the method of using the adsorbent of the present invention as a gas mask filler, the method of using the adsorbent of the present invention as a filter of an air cleaner, the adsorption of the present invention in a container containing water containing radioactive cesium. There is a method of adsorbing radioactive cesium in the presence of an agent.
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