JP2014169959A - Radioactive cesium processing system - Google Patents
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Abstract
【課題】放射性セシウムが溶存する排水からセシウムのみを高効率で回収して、放射性セシウムによる汚染水等を浄化することができ、しかも環境負荷が少ない放射性セシウム処理システムを実現する。
【解決手段】放射性セシウムが溶存する排水に錯形成反応手段を添加し水分子を全く有しない疎水性錯体を形成して放射性セシウムを不溶化させる工程と、固液分離手段により不溶化した放射性セシウムを分離回収する工程とを具え、前記錯形成反応手段は遺伝子組み替え微生物発酵による２−ピロン−４，６−ジカルボン酸（ＰＤＣ）であることを特徴とする放射性セシウム処理システムを提供して、上記課題を解決する。
【選択図】 図３[PROBLEMS] To realize a radioactive cesium treatment system capable of recovering only cesium from wastewater in which radioactive cesium is dissolved with high efficiency and purifying contaminated water by radioactive cesium and having a low environmental load.
SOLUTION: A step of adding a complex formation reaction means to waste water in which radioactive cesium is dissolved to form a hydrophobic complex having no water molecule to insolubilize radioactive cesium, and a step of separating the insoluble radioactive cesium by solid-liquid separation means Providing a radioactive cesium treatment system characterized in that the complex formation reaction means is 2-pyrone-4,6-dicarboxylic acid (PDC) produced by genetically modified microbial fermentation. Solve.
[Selection] Figure 3
Description
本願発明は、セシウムの処理システムに関し、なお詳しくは、原子力発電所その他の放射性物質使用施設等から発生する廃液及び排水その他に含有・付着する放射性セシウムを分離・回収するための方法に関する。 The present invention relates to a cesium treatment system, and more particularly to a method for separating and recovering radioactive cesium contained / attached to waste liquid and waste water generated from nuclear power plants and other facilities using radioactive materials.
放射性セシウム（137Ｃｓ）はその半減期が長く(30ａ)、核分裂反応で形成される大量の同位体の中の最大の放射性物質であり、２０１１年３月の東日本大震災に伴い原子力発電所において大量の放射性セシウムを含有する廃液が生じ、さらに大量の放射性セシウムが市街地、農地、山地、海洋など広範囲に散布拡散してこれを汚染するという重大事故が発生して、生活のあらゆる面で種々の支障をきたし人々の日常生活面のみでなく、工業生産、農業生産、漁業生産等に深刻な影響をおよぼしており、放射性セシウムの適正・迅速な処理は震災からの復興の要ともいうべき事態となっている。 Radioactive cesium ( 137 Cs) has a long half-life (30a) and is the largest radioactive material among a large number of isotopes formed by fission reactions. As a result, a serious accident occurs in which a large amount of radioactive cesium is dispersed and diffused over a wide area such as urban areas, farmland, mountains, and oceans, causing various problems in all aspects of life. As a result, it has a serious impact not only on the daily life of people but also on industrial production, agricultural production, fishery production, etc. Proper and prompt treatment of radioactive cesium is a situation that should be said to be the key to recovery from the earthquake disaster. It has become.
従来、例えば放射性廃液から放射性セシウムを除去するために、沈殿法またはイオン交換法が用いられてきた。沈殿法はイオン交換体ほど分離度が高くなく、しかも、溶液から沈殿固体を効果的に分離するのが困難なことが多い。最も一般的には有機イオン交換樹脂がセシウム除去に適したイオン交換体として使用されており、1980年代後半以降、分離度を高めるためにゼオライト鉱物が使用されている。
しかしながら、上記の技術は製造設備や実施にかかる費用も高く、現実的に工業的実施は、が困難なであった。
Conventionally, precipitation or ion exchange methods have been used, for example, to remove radioactive cesium from radioactive liquid waste. In precipitation methods, the degree of separation is not as high as that of ion exchangers, and it is often difficult to effectively separate the precipitated solid from the solution. Most commonly, organic ion exchange resins are used as ion exchangers suitable for cesium removal, and zeolite minerals have been used since the late 1980s to increase the degree of separation.
However, the above-described technology is expensive in terms of manufacturing equipment and implementation, and practically difficult to implement industrially.
また、遷移元素のヘキサシアノ鉄酸塩がセシウム結合イオン交換体として有機樹脂やゼオライトより優れていることは既に知られており、さらに、ゼオライト、有機樹脂、リンモリブデン酸アンモニウムと比較して、例えばヘキサシアノ鉄酸カリウムコバルトは高い交換効率を示している。リンモリブデン酸アンモニウムはセシウムの効率的なイオン交換体として認められているが、例えば核燃料再処理施設の濃縮ＮａＮＯ3溶液および原子力発電所の廃液蒸発残留物からのセシウムの除去において、ゼオライトや有機イオン交換樹脂には実際的な使用適性が認められていない。 In addition, it is already known that the transition element hexacyanoferrate is superior to organic resins and zeolites as a cesium-bonded ion exchanger. Furthermore, compared to zeolites, organic resins, and ammonium phosphomolybdate, for example, hexacyanoferrate Potassium cobalt ferrate shows high exchange efficiency. Ammonium phosphomolybdate has been recognized as an efficient ion exchanger for cesium, but for example, in the removal of cesium from concentrated NaNO 3 solutions in nuclear fuel reprocessing facilities and from the evaporation residue of nuclear power plant waste, There is no practical applicability to the exchange resin.
さらに、多くのイオン交換樹脂等のイオン交換化合物と結合させてカラムでの使用に適したヘキサシアノ鉄酸塩を製造する方法が開発されてきたが、工業使用に採用された例はない。有機イオン交換樹脂に結合されたヘキサシアノ鉄酸塩は高線量に対する抵抗が大幅に低下するため、その結合力は少量の137Ｃｓ分離に制限されてしまう。 Furthermore, a method for producing hexacyanoferrate suitable for use in a column by combining with many ion exchange compounds such as ion exchange resins has been developed, but no example has been adopted for industrial use. Since hexacyanoferrate bound to an organic ion exchange resin has a greatly reduced resistance to high doses, its binding force is limited to a small amount of 137Cs separation.
上記のような見地に鑑みて、セシウム含有水溶液を遷移元素の固体ヘキサシアノ鉄酸塩化合物と接触させてセシウムをヘキサシアノ鉄酸塩と結合させ、セシウム含有量が減少した水溶液をヘキサシアノ鉄酸塩から分離する段階を含む、水溶液、特に核廃液からセシウムを除去する方法において、交換可能な遷移元素分が35％以下である遷移元素ヘキサシアノ鉄酸塩を用いる方法が、提案されている。 In view of the above, the cesium-containing aqueous solution is brought into contact with the transition element solid hexacyanoferrate compound to combine cesium with hexacyanoferrate, and the aqueous solution with reduced cesium content is separated from hexacyanoferrate. In a method of removing cesium from an aqueous solution, particularly a nuclear waste solution, including a step of performing a step, a method using a transition element hexacyanoferrate having an exchangeable transition element content of 35% or less has been proposed.
さらに、フェロシアン化鉄を使用してセシウムを吸着する方法も従来から提案実施されている。すなわち、セシウムを吸着する働きがある点に着目して、汚染水にこの顔料を混ぜ、遠心力で分離した後、セシウムとともにフィルターでこし取るシステムなどが知られている。 Furthermore, a method for adsorbing cesium using ferric ferrocyanide has been proposed and implemented. That is, paying attention to the function of adsorbing cesium, a system is known in which this pigment is mixed with contaminated water, separated by centrifugal force, and then scraped with a filter together with cesium.
本願に関連して、以下の技術文献が存在する。
しかしながら、上記従来の処理技術に用いられている吸着原料については安全性ならびに環境汚染の点で問題なしと言えず、より安全なセシウム処理技術が求められている。特に現在セシウム除去にもっとも有望視されているフェロシアン化鉄を利用した汚染水浄化技術は大量のフェロシアン化鉄の投入を必要とするためシアン化合物に変換され環境汚染に繋がるおそれがある。 However, the adsorbing raw materials used in the above-described conventional processing technology cannot be said to have no problem in terms of safety and environmental pollution, and a safer cesium processing technology is required. In particular, the contaminated water purification technology using ferrocyanide, which is currently most promising for cesium removal, requires the input of a large amount of ferrocyanide, so it may be converted to cyanide and lead to environmental pollution.
発明の背景
（１族の）アルカリ金属は水に溶けやすく、錯体を形成する化合物はあまり見つかっていない。リグニン低分子芳香族化合物から組換え微生物を用いてPDCを生産する技術は、プラスチック原料などを目的として既に発明者らが開発済みであるが（特許第４９１４０４１号）、その発酵生産の過程でアルカリ金属であるNaと錯体を形成して沈殿を生ずることが知見されていた。
BACKGROUND OF THE INVENTION Alkali metals (Group 1) are readily soluble in water, and few compounds that form complexes have been found. The technology for producing PDC from lignin low-molecular aromatic compounds using recombinant microorganisms has already been developed by the inventors for the purpose of plastic raw materials (Japanese Patent No. 4914041). It has been found that a precipitate is formed by forming a complex with Na, which is a metal.
ところで、東京電力福島第１原発の事故以降問題となっている放射性セシウム汚染において、CsもNaと同じアルカリ金属であることから、PDCを添加することによってセシウムと錯体を形成し水溶液中からセシウムを沈殿除去出来るかを検討した。その結果PDCはNaよりもCsと優先的に錯体を形成し、選択的な沈殿除去が可能であることが判明した。PDC-Cs錯体の構造をX線結晶回折により分析・同定したところ、Ｃｓ+イオンの周りに，１プロトン化したＰＤＣ（Hpdc-）アニオン７分子からの８個の酸素原子が配位結合している構造をしており， 2つのNa原子に対して4つのPDC分子と6つの水分子が相互作用するPDC-Na錯体とは全く異なる錯体構造であることが明らかとなった。 By the way, in the radioactive cesium pollution that has been a problem since the accident at the TEPCO Fukushima Daiichi nuclear power plant, Cs is the same alkali metal as Na. It was examined whether precipitation could be removed. As a result, it was found that PDC forms a complex with Cs preferentially over Na and can selectively remove precipitates. The structure of the PDC-Cs complex was analyzed and identified by X-ray crystal diffraction. As a result, eight oxygen atoms from seven protonated PDC (Hpdc − ) anions coordinated around the Cs + ion. It was revealed that the complex structure is completely different from the PDC-Na complex in which four PDC molecules and six water molecules interact with two Na atoms.
この構造の違いから、水分子を全く含まず頼大きな錯体分子となるPDC-Cs錯体は、非常に疎水的で沈殿しやすく、Naを含む溶液中でも優先的にPDC-Cs錯体が沈殿として回収されることが理解できる。またPDCは、従来セシウム吸着剤として使用されてきたフェロシアン化鉄とは異なり、土壌微生物による芳香族化合物の中間代謝物であるために大量に使用して環境中に放出されても環境負荷が少なく、大胆な大量投与も可能と考えられる。 以上の背景の下において本願発明がなされるにいたった。 Because of this difference in structure, PDC-Cs complexes that do not contain any water molecules and become large complex molecules are very hydrophobic and easily precipitate, and PDC-Cs complexes are preferentially recovered as precipitates even in solutions containing Na. I can understand. Unlike ferric ferrocyanide, which has been used as a cesium adsorbent, PDC is an intermediate metabolite of aromatic compounds by soil microorganisms. There are few, bold, large doses possible. The present invention has been made under the above background.
本願発明は、上記従来の課題を解決するためになされたもので、 放射性セシウムが溶存する排水に錯形成反応手段を添加し水分子を全く有しない疎水性錯体を形成して放射性セシウムを不溶化させる工程と、固液分離手段により不溶化した放射性セシウムを分離回収する工程とを具えてなる放射性セシウム処理システムを提供して、上記従来の課題を解決しようとするものである。 The present invention has been made in order to solve the above-described conventional problems. A complexation reaction means is added to wastewater in which radioactive cesium is dissolved to form a hydrophobic complex having no water molecules, thereby insolubilizing radioactive cesium. An object of the present invention is to provide a radioactive cesium treatment system comprising a step and a step of separating and recovering radioactive cesium insolubilized by a solid-liquid separation means, and intends to solve the above conventional problems.
また、上記段落００１３記載の放射性セシウム処理システムにおいて、前記錯形成反応手段は遺伝子組み替え微生物発酵による２−ピロン−４，６−ジカルボン酸（ＰＤＣ）で構成することがある。 In the radioactive cesium treatment system described in paragraph 0013 above, the complexation reaction means may be composed of 2-pyrone-4,6-dicarboxylic acid (PDC) by genetically modified microbial fermentation.
さらに、上記段落００１４記載の排水処理システムにおいて、前記、２−ピロン−４，６−ジカルボン酸（ＰＤＣ）の添加はセシウムに対して概ね６倍モル以上となすことがある。 Furthermore, in the wastewater treatment system described in paragraph 0014 above, the addition of 2-pyrone-4,6-dicarboxylic acid (PDC) may be approximately 6 times or more moles relative to cesium.
またさらに、上記段落００１５記載の排水処理システムにおいて、固液分離手段を分子量分画膜により構成して放射性セシウムを前記２−ピロン−４，６−ジカルボン酸（ＰＤＣ）とにより形成され液中に滞留する錯体分子を捕捉して放射性セシウムを分離回収するように構成することがある。 Furthermore, in the wastewater treatment system according to paragraph 0015, the solid-liquid separation means is constituted by a molecular weight fractionation membrane, and radioactive cesium is formed with the 2-pyrone-4,6-dicarboxylic acid (PDC). There are cases where the complex molecules staying are captured and the radioactive cesium is separated and recovered.
本願発明はまた、放射性セシウムに汚染された土壌、焼却灰に水分を添加して放射性セシウムを水分中に溶存させる工程と、前記工程による放射性セシウム水溶液に錯形成反応手段を添加し水分子を全く有しない疎水性錯体を形成して放射性セシウムを不溶化させる工程と、固液分離手段により不溶化した放射性セシウムを分離回収する工程と、を具えてなる放射性セシウム処理システムを、提供する。 The present invention also includes soil contaminated with radioactive cesium, a step of adding moisture to incineration ash to dissolve the radioactive cesium in the moisture, and adding a complex formation reaction means to the radioactive cesium aqueous solution by the above step to completely remove water molecules. Provided is a radioactive cesium treatment system comprising a step of insolubilizing radioactive cesium by forming a hydrophobic complex that does not have, and a step of separating and recovering radioactive cesium insolubilized by solid-liquid separation means.
また、上記段落００１７記載の放射性セシウム処理システムにおいて、前記錯形成反応手段は遺伝子組み替え微生物発酵による２−ピロン−４，６−ジカルボン酸（ＰＤＣ）で構成することがある。 In the radioactive cesium treatment system described in paragraph 0017 above, the complexing reaction means may be composed of 2-pyrone-4,6-dicarboxylic acid (PDC) by genetically modified microbial fermentation.
さらに、上記段落００１８記載の放射性セシウム処理システムにおいて、前記２−ピロン−４，６−ジカルボン酸（ＰＤＣ）の添加はセシウムに対して概ね６倍モル以上となすことがある。 Furthermore, in the radioactive cesium treatment system described in paragraph 0018 above, the addition of 2-pyrone-4,6-dicarboxylic acid (PDC) may be approximately 6 times or more moles of cesium.
またさらに、上記段落００１９記載の放射性セシウム処理システムにおいて、固液分離手段を分子量分画膜により構成して放射性セシウムを前記２−ピロン−４，６−ジカルボン酸（ＰＤＣ）とにより形成され液中に滞留する錯体分子を捕捉して放射性セシウムを分離回収するように構成することがある。 Furthermore, in the radioactive cesium treatment system described in paragraph 0019 above, the solid-liquid separation means is constituted by a molecular weight fractionation membrane, and the radioactive cesium is formed with the 2-pyrone-4,6-dicarboxylic acid (PDC). In some cases, the radioactive cesium is separated and recovered by capturing the complex molecules staying in the substrate.
本願発明は、以上の構成により、放射性セシウムが溶存する排水からセシウムのみを高効率で回収して、放射性セシウムによる汚染水等を浄化することができ、しかも組み替え微生物発酵により生産された２−ピロン−４，６−ジカルボン酸（ＰＤＣ）は土壌細菌の中間代謝物であるため大量使用しても環境負荷が少ない。 The invention of the present application has the above configuration, and can recover only cesium from wastewater in which radioactive cesium is dissolved, purify contaminated water by radioactive cesium, and is produced by recombinant microbial fermentation. Since -4,6-dicarboxylic acid (PDC) is an intermediate metabolite of soil bacteria, it has little environmental impact even when used in large quantities.
本願発明において、セシウムに係る水分子を全く有しない疎水性錯体を形成するための錯
形成反応手段としては遺伝子組み替え微生物発酵による２−ピロン−４，６−ジカルボン酸（ＰＤＣ）が望ましい。 そして、放射性セシウムが溶存する排水への前記２−ピロン−４，６−ジカルボン酸（ＰＤＣ）の添加はセシウムに対して概ね６倍モル以上であることが好ましい。
In the present invention, 2-pyrone-4,6-dicarboxylic acid (PDC) produced by genetically modified microorganism fermentation is desirable as a complex formation reaction means for forming a hydrophobic complex having no water molecule related to cesium. And it is preferable that the addition of the 2-pyrone-4,6-dicarboxylic acid (PDC) to the waste water in which radioactive cesium is dissolved is approximately 6 times mol or more with respect to cesium.
また、放射性セシウムが存在する汚染水の浄化については、前記２−ピロン−４，６−ジカルボン酸（ＰＤＣ）の適量添加により放射性セシウムとの錯体形成によりこれを水中に沈殿させて回収するが、放射性セシウムに汚染された土壌、焼却灰等については水分を添加して放射性セシウムを水分中に溶存させて、前述の工程により放射性セシウムを回収することになる。 In addition, for purification of contaminated water in which radioactive cesium is present, the appropriate amount of 2-pyrone-4,6-dicarboxylic acid (PDC) is added to form a complex with radioactive cesium by precipitation and recovered. About soil contaminated with radioactive cesium, incineration ash, etc., water is added to dissolve the radioactive cesium in the moisture, and the radioactive cesium is recovered by the above-described process.
水中に沈殿した錯体は遠心分離機あるいはろ過手段などの固液分離手段により分離回収することになるが、Ｃｓ濃度が低く錯体が沈殿せず水中に滞留している状況では固液分離手段として分子量分画膜を使用する。 前記の各固液分離手段を併用することもある。 The complex precipitated in water is separated and recovered by a solid-liquid separation means such as a centrifuge or a filtration means. However, in the situation where the Cs concentration is low and the complex is not precipitated and remains in water, the molecular weight is used as the solid-liquid separation means. Use a membrane. The above-mentioned solid-liquid separation means may be used in combination.
以下の試験において、ＰＤＣは特許第４９１４０４１号に係る製法により生産したものを使用した。
実験例１
（イ） 最終濃度PDC 500mM (7.5 wt%)、Cs
50mM (0.66 wt%)となるPDC-Cs混合溶液を調製した。
（ロ） 最終濃度PDC 500mM (7.5 wt%)、Na
50mM (0.14 wt%)となるPDC-Na混合溶液を調製した。
（ハ） 上記（イ）、（ロ）の両混合溶液を室温で５分間攪拌しながら観察したところ、前記（イ）のPDC-Cs混合溶液においてのみ錯体形成による沈殿が観察された。
In the following tests, PDC produced by the manufacturing method according to Japanese Patent No. 4914041 was used.
Experimental example 1
(B) Final concentration PDC 500 mM (7.5 wt%), Cs
A PDC-Cs mixed solution of 50 mM (0.66 wt%) was prepared.
(B) Final concentration PDC 500mM (7.5 wt%), Na
A PDC-Na mixed solution of 50 mM (0.14 wt%) was prepared.
(C) When both of the mixed solutions (a) and (b) were observed at room temperature with stirring for 5 minutes, precipitation due to complex formation was observed only in the PDC-Cs mixed solution of (a).
実験例２
（イ） 塩化セシウム(CsCl)を純水に溶解した塩化セシウム水溶液、塩化ナトリウム(NaCl)を純水に溶解した塩化ナトリウム水溶液を準備し、様々な濃度で混合してCs沈殿除去効果を検討した。混合溶液は室温で５分間攪拌した後一晩静置した。
（ロ） 遠心分離によって不溶化したPDC-Cs錯体を除去し上清を回収した。さらに不溶化したPDC-Cs錯体を完全に除くため0.45μmのフィルターで濾過した。濾液に最終濃度1.2%になるよう硝酸（60%金属分析用硝酸溶液）を加え、ICP-MSにより残存Cs量を測定したところ、図１の表に示すようにCs濃度が50mM (0.66%)では98.25%、5mM (0.066%)でも92.1%と高い除去率を示した。また、CsおよびNaを50mMずつ含む溶液中においても95.9%の除去率を示し、Cs 5mM(0.066%)でNaを50mM (10倍)含む場合でも88.85%と高い除去率を示した。
Experimental example 2
(B) Cesium chloride aqueous solution in which cesium chloride (CsCl) was dissolved in pure water and sodium chloride aqueous solution in which sodium chloride (NaCl) was dissolved in pure water were prepared and mixed at various concentrations to examine the Cs precipitation removal effect. . The mixed solution was stirred at room temperature for 5 minutes and then allowed to stand overnight.
(B) The PDC-Cs complex insolubilized by centrifugation was removed and the supernatant was recovered. Further, in order to completely remove the insolubilized PDC-Cs complex, it was filtered with a 0.45 μm filter. Nitric acid (60% metal analysis nitric acid solution) was added to the filtrate to a final concentration of 1.2%, and the residual Cs content was measured by ICP-MS. As shown in the table of FIG. 1, the Cs concentration was 50 mM (0.66%). Showed high removal rate of 92.1% at 98.25% and 5mM (0.066%). In addition, the removal rate was 95.9% even in a solution containing 50 mM of Cs and Na. Even when Cs was 5 mM (0.066%) and Na was contained 50 mM (10 times), the removal rate was as high as 88.85%.
実験例３
模擬汚染土壌からセシウム（Cs）の選択的沈殿
セシウム（塩化セシウム）を１％含有する模擬汚染土壌（褐色森林土）を用いた。模擬汚染土壌100gに対し水500mlを加えて懸濁状態とし、さらに0.5規定の酸溶液（塩酸溶液、硝酸溶液等）を加えて酸性とした。この懸濁液を濾過して水層を捕集した。
さらに、この懸濁、酸性化抽出操作を３回繰り返して、得られた水層を併せた後、容量を測定した。この溶液に最終濃度が7.5%となるようにPDCを加え、室温で1時間放置した後、PDC-Cs錯体を形成させ、沈殿としてPDC-Cs錯体を回収した。セシウム除去率は水層に溶出したセシウム量の98%であった。
Experimental example 3
Preferential precipitation of cesium (Cs) from simulated contaminated soil Simulated contaminated soil (brown forest soil) containing 1% cesium (cesium chloride) was used. To 100 g of simulated contaminated soil, 500 ml of water was added to make a suspended state, and 0.5 N acid solution (hydrochloric acid solution, nitric acid solution, etc.) was added to make it acidic. This suspension was filtered to collect the aqueous layer.
Further, this suspension and acidification extraction operation was repeated three times, and the obtained aqueous layer was combined, and then the volume was measured. PDC was added to this solution to a final concentration of 7.5%, and the mixture was allowed to stand at room temperature for 1 hour. Then, a PDC-Cs complex was formed, and the PDC-Cs complex was recovered as a precipitate. The cesium removal rate was 98% of the amount of cesium eluted in the aqueous layer.
実験例４
模擬焼却灰からセシウム（Cs）の選択的沈殿
木材または木炭を灰化させて得られた焼却灰1gにセシウム（塩化セシウム）を100mg添加して混合したものを模擬汚染焼却灰とした。この模擬汚染焼却灰に水100mlを加えて懸濁状態とし、さらに0.5規定の酸溶液（塩酸溶液、硝酸溶液等）を加えて酸性とした。焼却灰懸濁液を遠心分離して、上清を捕集した。焼却灰沈殿物に水100ml、0.5規定の酸溶液を加えて懸濁状態とした後、再び遠心分離して上清を捕集した。この操作を２回繰り返し、得られた上清を併せて、焼却灰抽出液とした。この抽出液の容量を測定後、最終濃度が7.5%となるようにPDCを加え、室温で1時間放置した後、PDC-Cs錯体を形成させ、沈殿としてPDC-Cs錯体を回収した。セシウム除去率は水層に溶出したセシウム量の99%であった。
Experimental Example 4
Selective precipitation of cesium (Cs) from simulated incineration ash 100 mg of cesium (cesium chloride) added to 1 g of incineration ash obtained by ashing wood or charcoal was used as simulated incineration ash. 100 ml of water was added to the simulated contaminated incineration ash to make it into a suspended state, and 0.5N acid solution (hydrochloric acid solution, nitric acid solution, etc.) was added to make it acidic. The incinerated ash suspension was centrifuged and the supernatant was collected. The incinerated ash precipitate was suspended by adding 100 ml of water and a 0.5 N acid solution, and then centrifuged again to collect the supernatant. This operation was repeated twice, and the resulting supernatant was combined into an incinerated ash extract. After measuring the volume of this extract, PDC was added to a final concentration of 7.5%, and the mixture was allowed to stand at room temperature for 1 hour. Then, a PDC-Cs complex was formed, and the PDC-Cs complex was recovered as a precipitate. The cesium removal rate was 99% of the amount of cesium eluted in the aqueous layer.
実験例５
低濃度汚染水から分子量分画によるセシウム（Cs）の選択的除去
セシウム濃度10ppmに調整した水溶液100mlに0.5MPDC水溶液10mlを添加し、室温で１時間ゆっくりと攪拌し錯体形成させた。セシウムが低濃度のため沈殿は観察されなかった。この混合液をPall Corporation製のMinimate TFF Capsule with Omega 1K Membrane （分子量1000以上を捕捉する分子量分画膜）に毎分10mlの流速で１時間循環させることにより、混合液中のPDC-Cs錯体を捕捉した。処理後の混合液に最終濃度1.2％になるように硝酸（60%金属分析用硝酸溶液）を加え、ICP-MSにより残存Cs量を測定した。その結果、水溶液中のセシウムの99％以上を除去することができた。
Experimental Example 5
Selective removal of cesium (Cs) from low-concentration contaminated water by molecular weight fractionation 10 ml of 0.5MPDC aqueous solution was added to 100 ml of an aqueous solution adjusted to a cesium concentration of 10 ppm, and the mixture was slowly stirred for 1 hour at room temperature to form a complex. No precipitation was observed due to the low concentration of cesium. This mixture is circulated through Pall Corporation's Minimate TFF Capsule with Omega 1K Membrane (a molecular weight fractionation membrane that captures a molecular weight of 1000 or more) for 1 hour at a flow rate of 10 ml / min. Captured. Nitric acid (60% nitric acid solution for metal analysis) was added to the mixed solution after treatment to a final concentration of 1.2%, and the amount of residual Cs was measured by ICP-MS. As a result, 99% or more of cesium in the aqueous solution could be removed.
以上の結果から0.5wt％以上の濃度（5000ppm以上）で水に溶解したCsに対してはPDCを添加することによって錯体として沈殿させることができ、濾過などの処理によって良好に除去出来ることが明らかとなった。また水溶液中にNaが混在していてもCsと優先的に錯体を形成し良好に沈殿除去出来ることが明らかとなった。
またPDC-Cs錯体結晶のX線結晶回折分析から、図２の構造式に示すようにPDC-Cs錯体は２つのCs原子に対して12のPDC分子が相互作用する分子量2500程度の非常に大きな錯体を形成することが判明した。
From the above results, it is clear that Cs dissolved in water at a concentration of 0.5 wt% or more (5000 ppm or more) can be precipitated as a complex by adding PDC and can be removed well by filtration and other treatments. It became. It was also found that even if Na was mixed in the aqueous solution, it could form a complex preferentially with Cs and precipitate well.
Also, from the X-ray crystal diffraction analysis of the PDC-Cs complex crystal, as shown in the structural formula of Fig. 2, the PDC-Cs complex has a very large molecular weight of about 2500 where 12 PDC molecules interact with 2 Cs atoms. It was found to form a complex.
図２および図３の構造式から明らかなように、PDC-Na錯体は２つのNa原子に対して4のPDC分子と6の水分子が相互作用する比較的低分子量で水分子を含む水和物である。水分子を全く含まず非常に大きな分子となるPDC-Cs錯体はPDC-Na錯体と比較して非常に沈殿しやすいことから、Naを含む溶液中であっても優先的にCsがPDCとPDC-Cs錯体を形成し、沈殿として回収できることが明らかとなった。 As is clear from the structural formulas of FIGS. 2 and 3, the PDC-Na complex is a hydrated water molecule with a relatively low molecular weight in which 4 PDC molecules and 6 water molecules interact with each other for 2 Na atoms. It is a thing. PDC-Cs complexes that do not contain any water molecules and become very large molecules are much easier to precipitate than PDC-Na complexes, so Cs is preferentially PDC and PDC even in solutions containing Na. It was found that -Cs complex can be formed and recovered as a precipitate.
ところで、Cs濃度が0.5wt%以下（5000ppm以下）の場合はPDCと混合しても沈殿として回収できない場合がある。しかしながら、このような場合であってもPDCとCsは錯体を形成し高分子として水溶液中に存在している。そのため例えば分子量１０００程度以上を捕捉するような分子量分画膜で水溶液中のPDC-Cs錯体を捕集することにより、良好にCsを回収することができることが明らかとなった。 By the way, when the Cs concentration is 0.5 wt% or less (5000 ppm or less), it may not be recovered as a precipitate even when mixed with PDC. However, even in such a case, PDC and Cs form a complex and exist in the aqueous solution as a polymer. Therefore, for example, it was revealed that Cs can be recovered satisfactorily by collecting the PDC-Cs complex in the aqueous solution with a molecular weight fractionation film that captures a molecular weight of about 1000 or more.
以上の結果から水に溶解したCsにPDCを添加することによって良好に錯体として沈殿除去出来ることが明らかとなり、また水溶液中にNaが混在していてもCsと優先的に錯体を形成し良好に沈殿除去出来ることが明らかとなった。
またPDC-Cs錯体結晶のX線結晶回折分析から、図２の構造式に示すようにPDC-Cs錯体は２つのCs原子に対して12のPDC分子が相互作用する非常に大きな錯体を形成することが判明した。
From the above results, it is clear that by adding PDC to Cs dissolved in water, it is possible to precipitate and remove well as a complex, and even if Na is mixed in the aqueous solution, it preferentially forms a complex with Cs, which is favorable. It became clear that precipitation could be removed.
From the X-ray crystal diffraction analysis of the PDC-Cs complex crystal, as shown in the structural formula of Fig. 2, the PDC-Cs complex forms a very large complex in which 12 PDC molecules interact with two Cs atoms. It has been found.
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| US4764281A (en) * | 1986-04-07 | 1988-08-16 | Iso-Clear Systems Corporation | Method of removing radioactive isotopes of heavy metals |
| JP2006346544A (en) * | 2005-06-14 | 2006-12-28 | Asahi Kasei Chemicals Corp | Ion removal apparatus and ion removal method |
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