JP6300197B2 - Method for stabilizing radioactive cesium adsorbed on ferrocyanide - Google Patents
Method for stabilizing radioactive cesium adsorbed on ferrocyanide Download PDFInfo
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- JP6300197B2 JP6300197B2 JP2014011466A JP2014011466A JP6300197B2 JP 6300197 B2 JP6300197 B2 JP 6300197B2 JP 2014011466 A JP2014011466 A JP 2014011466A JP 2014011466 A JP2014011466 A JP 2014011466A JP 6300197 B2 JP6300197 B2 JP 6300197B2
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- 229910052792 caesium Inorganic materials 0.000 title claims description 36
- TVFDJXOCXUVLDH-UHFFFAOYSA-N caesium atom Chemical compound [Cs] TVFDJXOCXUVLDH-UHFFFAOYSA-N 0.000 title claims description 31
- 238000000034 method Methods 0.000 title claims description 14
- 230000002285 radioactive effect Effects 0.000 title claims description 10
- 230000000087 stabilizing effect Effects 0.000 title claims description 6
- 238000010304 firing Methods 0.000 claims description 20
- 229920000876 geopolymer Polymers 0.000 claims description 16
- 239000003513 alkali Substances 0.000 claims description 12
- 239000012190 activator Substances 0.000 claims description 6
- 238000000354 decomposition reaction Methods 0.000 claims description 6
- NTHWMYGWWRZVTN-UHFFFAOYSA-N sodium silicate Chemical compound [Na+].[Na+].[O-][Si]([O-])=O NTHWMYGWWRZVTN-UHFFFAOYSA-N 0.000 claims description 6
- 239000000945 filler Substances 0.000 claims description 5
- 239000010881 fly ash Substances 0.000 claims description 5
- 239000004115 Sodium Silicate Substances 0.000 claims description 4
- NLYAJNPCOHFWQQ-UHFFFAOYSA-N kaolin Chemical compound O.O.O=[Al]O[Si](=O)O[Si](=O)O[Al]=O NLYAJNPCOHFWQQ-UHFFFAOYSA-N 0.000 claims description 4
- 239000000203 mixture Substances 0.000 claims description 4
- 229910052911 sodium silicate Inorganic materials 0.000 claims description 4
- 239000000243 solution Substances 0.000 claims description 4
- 238000006243 chemical reaction Methods 0.000 claims description 3
- 230000006641 stabilisation Effects 0.000 claims description 3
- 238000011105 stabilization Methods 0.000 claims description 3
- 229910052723 transition metal Inorganic materials 0.000 claims description 3
- 150000003624 transition metals Chemical class 0.000 claims description 3
- 239000007864 aqueous solution Substances 0.000 claims description 2
- 238000000465 moulding Methods 0.000 claims 1
- 239000000047 product Substances 0.000 description 27
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 13
- 239000000463 material Substances 0.000 description 11
- 238000010828 elution Methods 0.000 description 7
- 238000002386 leaching Methods 0.000 description 7
- 238000005033 Fourier transform infrared spectroscopy Methods 0.000 description 6
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 6
- 229910052742 iron Inorganic materials 0.000 description 6
- 238000000550 scanning electron microscopy energy dispersive X-ray spectroscopy Methods 0.000 description 6
- 239000004568 cement Substances 0.000 description 5
- XFXPMWWXUTWYJX-UHFFFAOYSA-N Cyanide Chemical compound N#[C-] XFXPMWWXUTWYJX-UHFFFAOYSA-N 0.000 description 4
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 4
- 238000010586 diagram Methods 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 3
- MWUXSHHQAYIFBG-UHFFFAOYSA-N Nitric oxide Chemical compound O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 3
- 238000003672 processing method Methods 0.000 description 3
- 238000004445 quantitative analysis Methods 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- AIYUHDOJVYHVIT-UHFFFAOYSA-M caesium chloride Chemical compound [Cl-].[Cs+] AIYUHDOJVYHVIT-UHFFFAOYSA-M 0.000 description 2
- 238000001354 calcination Methods 0.000 description 2
- -1 cesium ions Chemical class 0.000 description 2
- 229910017052 cobalt Inorganic materials 0.000 description 2
- 239000010941 cobalt Substances 0.000 description 2
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 2
- 239000012153 distilled water Substances 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 238000013507 mapping Methods 0.000 description 2
- 229910052759 nickel Inorganic materials 0.000 description 2
- LGQLOGILCSXPEA-UHFFFAOYSA-L nickel sulfate Chemical compound [Ni+2].[O-]S([O-])(=O)=O LGQLOGILCSXPEA-UHFFFAOYSA-L 0.000 description 2
- 229910000363 nickel(II) sulfate Inorganic materials 0.000 description 2
- 239000008188 pellet Substances 0.000 description 2
- 239000000276 potassium ferrocyanide Substances 0.000 description 2
- 235000019353 potassium silicate Nutrition 0.000 description 2
- 229910052710 silicon Inorganic materials 0.000 description 2
- 239000010703 silicon Substances 0.000 description 2
- 239000011734 sodium Substances 0.000 description 2
- 229910001415 sodium ion Inorganic materials 0.000 description 2
- 238000007711 solidification Methods 0.000 description 2
- 230000008023 solidification Effects 0.000 description 2
- 230000003595 spectral effect Effects 0.000 description 2
- XOGGUFAVLNCTRS-UHFFFAOYSA-N tetrapotassium;iron(2+);hexacyanide Chemical compound [K+].[K+].[K+].[K+].[Fe+2].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-] XOGGUFAVLNCTRS-UHFFFAOYSA-N 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 240000007594 Oryza sativa Species 0.000 description 1
- 235000007164 Oryza sativa Nutrition 0.000 description 1
- 239000011398 Portland cement Substances 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 239000003463 adsorbent Substances 0.000 description 1
- 239000012670 alkaline solution Substances 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 239000002956 ash Substances 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 238000001784 detoxification Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000010903 husk Substances 0.000 description 1
- 230000003100 immobilizing effect Effects 0.000 description 1
- 229910010272 inorganic material Inorganic materials 0.000 description 1
- 239000011147 inorganic material Substances 0.000 description 1
- 238000004898 kneading Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 239000007800 oxidant agent Substances 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 238000002203 pretreatment Methods 0.000 description 1
- 235000009566 rice Nutrition 0.000 description 1
- 239000002893 slag Substances 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000006228 supernatant Substances 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
- 238000004017 vitrification Methods 0.000 description 1
- 238000004056 waste incineration Methods 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P40/00—Technologies relating to the processing of minerals
- Y02P40/10—Production of cement, e.g. improving or optimising the production methods; Cement grinding
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
- Y02W30/91—Use of waste materials as fillers for mortars or concrete
Landscapes
- Solid-Sorbent Or Filter-Aiding Compositions (AREA)
- Curing Cements, Concrete, And Artificial Stone (AREA)
Description
本発明は、フェロシアン化物に吸着した放射性セシウムの安定化処理方法に関するものである。 The present invention relates to a method for stabilizing radioactive cesium adsorbed on a ferrocyanide.
難溶性のフェロシアン化物は、セシウムイオンの選択吸着能力が高いことから、セシウムの吸着材として広く利用されている。しかし、フェロシアン化物は熱やアルカリに不安定であり、分解温度は３００℃〜４００℃程度で、雰囲気によっては有害なシアンガスが発生することが報告されている。また、高アルカリにより、一部シアン化物イオンが遊離することも報告されている。 Slightly soluble ferrocyanides are widely used as cesium adsorbents because of their high selective adsorption ability of cesium ions. However, it is reported that ferrocyanide is unstable to heat and alkali, the decomposition temperature is about 300 ° C. to 400 ° C., and harmful cyan gas is generated depending on the atmosphere. It has also been reported that some cyanide ions are liberated by high alkali.
フェロシアン化物はアルカリ溶液と懸濁し、酸化剤を添加して湿式処理により酸化分解するが、一度吸着したセシウムが再度溶離してしまう懸念がある。また、酸化雰囲気で加熱することにより、シアン成分を二酸化炭素と窒素酸化物まで分解できるが、単独で加熱した場合、遊離したセシウムが揮散する懸念がある。 Ferrocyanide is suspended in an alkali solution and oxidatively decomposed by wet treatment with the addition of an oxidizing agent, but there is a concern that cesium once adsorbed will be eluted again. In addition, although the cyan component can be decomposed into carbon dioxide and nitrogen oxide by heating in an oxidizing atmosphere, there is a concern that liberated cesium is volatilized when heated alone.
このようなことから、無害化処理に伴い遊離するセシウムを固定化できるフェロシアン化物の前処理方法の開発が必要となっている。 For this reason, it is necessary to develop a pretreatment method for ferrocyanide capable of immobilizing cesium liberated with the detoxification treatment.
なお、放射性セシウム汚染物の処理方法に関する先行技術としては、例えば下記の特許文献１〜４などを挙げることができる。 In addition, as a prior art regarding the processing method of radioactive cesium contamination, the following patent documents 1-4 etc. can be mentioned, for example.
セシウムを吸着したフェロシアン化物を安定固化する場合、セメントで固化する方法が考えられるが、セメント自体がアルカリのためシアンの溶出、あるいはそれに伴うセシウムの溶出が懸念される。 In order to solidify the ferrocyanide adsorbed with cesium stably, a method of solidifying with cement is conceivable. However, since the cement itself is alkali, there is a concern about elution of cyanide or accompanying cesium.
またガラス固化などの加熱（＞１０００℃）を伴う固化法では、固化の過程でシアンを無害化して、かつマトリクス中にセシウムを安定化することが可能であるが、高温処理時のセシウムの揮散が懸念される。 In addition, in solidification methods involving heating (> 1000 ° C) such as vitrification, it is possible to detoxify cyan during the solidification process and stabilize cesium in the matrix, but cesium volatilization during high temperature treatment Is concerned.
本発明の目的は、このような従来技術の欠点を解消し、フェロシアン化物を分解してシアンの溶出をなくし、かつ、遊離したＣｓを安定して固定化できるフェロシアン化物に吸着した放射性セシウムの安定化処理方法を提供することにある。 The object of the present invention is to eliminate the disadvantages of the prior art, eliminate the elution of cyanide by decomposing the ferrocyanide, and adsorb the radioactive cesium adsorbed on the ferrocyanide that can stably fix the liberated Cs. It is in providing the stabilization processing method of this.
前記目的を達成するため、本発明の第１の手段は、セシウムを吸着したフェロシアン化物とジオポリマーを混合して成形し、この成形物を前記フェロシアン化物の分解温度以上である３２０℃〜６００℃で焼成することにより、前記フェロシアン化物を分解し、かつ前記フェロシアン化物から遊離した前記セシウムを焼成物内で固定させることを特徴とするものである。 To achieve the above object, the first aspect of the present invention, by forming a mixture of ferrocyanide and geopolymeric adsorbed cesium, the molded product is a decomposition temperature or more of the ferrocyanide 320 ° C. ~ by baking at 600 ° C., to decompose the ferrocyanide, and is characterized in that to fix the cesium liberated from the ferrocyanide in the sintered product.
本発明の第２の手段は前記第１の手段において、前記フェロシアン化物が、例えばフェロシアン化ニッケル、フェロシアン化鉄、フェロシアン化コバルトなどのフェロシアン化遷移金属であることを特徴とするものである。 According to a second means of the present invention, in the first means, the ferrocyanide is a ferrocyanide transition metal such as nickel ferrocyanide, iron ferrocyanide, cobalt ferrocyanide and the like. Is.
本発明の第３の手段は前記第１または第２の手段において、前記ジオポリマーが、フィラーとアルカリ活性剤が反応して生成される３次元の網目構造を有するものであって、前記フィラーとしてメタカオリンまたは（および）フライアッシュが用いられ、前記アルカリ活性剤として、ケイ酸ナトリウム水溶液とアルカリ溶液が用いられることを特徴とするものである。 According to a third means of the present invention, in the first or second means, the geopolymer has a three-dimensional network structure formed by a reaction between a filler and an alkali activator, Metakaolin or (and) fly ash is used, and an aqueous sodium silicate solution and an alkaline solution are used as the alkali activator.
本発明は前述のような構成になっており、フェロシアン化物を分解してシアンの溶出をなくし、かつ、遊離したＣｓをジオポリマー中で安定して固定化できるフェロシアン化物に吸着した放射性セシウムの安定化処理方法を提供することができる。 The present invention has the above-described configuration, and the radioactive cesium adsorbed on the ferrocyanide which decomposes the ferrocyanide to eliminate elution of cyanide and can stably fix the liberated Cs in the geopolymer. The stabilization processing method can be provided.
本発明では、セシウムを吸着したフェロシアン化物とジオポリマーを混合して任意の大きさの例えばペレット状に成形し、この成形物をフェロシアン化物の分解温度以上（例えば３２０℃〜６００℃）で焼成することにより、フェロシアン化物を分解し、かつ遊離したセシウムを焼成物内で安定化させる処理方法である。 In the present invention, a ferrocyanide adsorbed with cesium and a geopolymer are mixed and formed into a pellet of any size, for example, and the molded product is at or above the decomposition temperature of the ferrocyanide (eg, 320 ° C. to 600 ° C.). This is a treatment method in which ferrocyanide is decomposed by firing and liberated cesium is stabilized in the fired product.
本実施例で用いたフェロシアン化物は、例えば硫酸ニッケルとフェロシアン化カリウムより生成した。その後、生成したフェロシアン化物と塩化セシウム（ＣｓＣｌ）がモル比１：４となるように水中に加え攪拌し、セシウムを吸着させてＣｓフェロシアン化物を得た。 The ferrocyanide used in this example was produced from, for example, nickel sulfate and potassium ferrocyanide. Thereafter, the produced ferrocyanide and cesium chloride (CsCl) were added to water so as to have a molar ratio of 1: 4 and stirred to adsorb cesium to obtain Cs ferrocyanide.
ジオポリマーとは主にアルミニウムとケイ素で構成されたアモルファス状の無機材料であり、フィラーとアルカリ活性剤が反応して生成される３次元の網目構造を有する固化体である。 The geopolymer is an amorphous inorganic material mainly composed of aluminum and silicon, and is a solidified body having a three-dimensional network structure formed by a reaction between a filler and an alkali activator.
フィラーとして、例えばメタカオリン（２ＳｉＯ２・Ａｌ２Ｏ３）、高炉スラグ、もみ殻灰、フライアッシュ（以下、ＦＡと略記することもある）などのケイ素やアルミニウムに富んだ材料が用いられる。特にメタカオリンやフライアッシュが好適である。また、アルカリ活性剤として、ケイ酸ナトリウム水溶液（水ガラス）とアルカリ溶液（水酸化ナトリウム）が用いられる。 As the filler, for example, a material rich in silicon or aluminum such as metakaolin (2SiO 2 .Al 2 O 3 ), blast furnace slag, rice husk ash, fly ash (hereinafter sometimes abbreviated as FA) is used. In particular, metakaolin and fly ash are suitable. Moreover, sodium silicate aqueous solution (water glass) and alkali solution (sodium hydroxide) are used as an alkali activator.
ジオポリマーの材料として本実施例では、ＦＡと、ケイ酸ナトリウム（水ガラス）と、水酸化ナトリウムと、蒸留水を用いた。 In this example, FA, sodium silicate (water glass), sodium hydroxide, and distilled water were used as geopolymer materials.
ジオポリマーの主な性質として、セシウムの溶出を抑える閉じ込め性能が高いこと、１２００℃の高温に晒されても所定の強度を維持する耐熱性に優れていることなどが挙げられる。 The main properties of the geopolymer include high confinement performance that suppresses elution of cesium and excellent heat resistance that maintains a predetermined strength even when exposed to a high temperature of 1200 ° C.
下記の表１は本発明の実施例と比較例の試料組成を示す表で、単位はｗｔ％である。表中のＧＰ／０．６とＧＰ／０．９は、本実施例のものでＮａ２Ｏ／Ａｌ２Ｏ３の割合（ａｔ％）を示している。ＯＰＣは、ジオポリマーの代わりに普通ポルトランドセメントを使用した比較例である。また、ＦＣ−Ｃｓは、セシウムを吸着したフェロシアン化物を示している。
ジオポリマー固化物（ＧＰ固化物）およびセメント固化物（ＯＰＣ固化物）からなる材料を手練りで２分間混練した後、直径２８ｍｍで厚さ３ｍｍのペレット状に成形し、ＧＰは８０℃、ＯＰＣは２５℃で１日間養生した。その後、試料を５００℃、空気雰囲気で３時間焼成した。 A material composed of a geopolymer solidified material (GP solidified material) and a cement solidified material (OPC solidified material) was kneaded by hand kneading for 2 minutes, and then formed into a pellet shape having a diameter of 28 mm and a thickness of 3 mm. Was cured at 25 ° C. for 1 day. Thereafter, the sample was fired at 500 ° C. in an air atmosphere for 3 hours.
焼成前後の固化物について、フェロシアン化物の炭素窒素間の三重結合（ＣＮ結合）に由来する特徴的なピークを日本分光株式会社製 フーリェ変換赤外分光光度計 ＦＴ／ＩＲ４２００（以下、ＦＴ−ＩＲと略記する）により測定した。 For the solidified product before and after firing, a characteristic peak derived from a triple bond between carbon and nitrogen (CN bond) of ferrocyanide is a Fourier transform infrared spectrophotometer FT / IR4200 (hereinafter referred to as FT-IR) manufactured by JASCO Corporation. (Abbreviated as).
図１はＧＰ固化物、図２はＯＰＣ固化物の焼成前後のフーリェ変換赤外分光特性図で、両図とも（ａ）は焼成前、（ｂ）は焼成後の特性図である。 FIG. 1 is a Fourier transform infrared spectroscopic characteristic diagram before and after calcination of a GP solidified product, and FIG. 2 is a characteristic diagram before and after calcination.
このＦＴ−ＩＲの測定結果、両図とも（ａ）に示す焼成前に観察されたＣＮ結合に由来する2100Kaiser付近の特徴的なピークが、（ｂ）に示すように焼成後は消失していた。このことから、焼成によりジオポリマーとセメント中のフェロシアン化物がほぼ完全に熱分解したと推定される。 As a result of the FT-IR measurement, in both figures, a characteristic peak near 2100 Kaiser derived from the CN bond observed before firing shown in (a) disappeared after firing as shown in (b). . From this, it is presumed that the geopolymer and ferrocyanide in cement were almost completely thermally decomposed by firing.
また図２（ｂ）に示すようにＯＰＣ固化物では焼成後にピーク強度が増大し、熱変形が生じていると考えられるが、図１（ｂ）に示すようにＧＰ固化物ではプロファイルに大きな変化が見られず、焼成による構造変化はそれほど無かったと推定される。 Moreover, as shown in FIG. 2 (b), in the OPC solidified product, the peak intensity increases after firing, and it is considered that thermal deformation has occurred, but as shown in FIG. 1 (b), the GP solidified product has a large change in profile. It is estimated that there was not much structural change due to firing.
さらに、焼成後の固化物の表面の組成分析と元素マッピングを日本電子株式会社製 走査型電子顕微鏡 ＪＳＭ−６０１０ＬＡ（以下、ＳＥＭ−ＥＤＸと略記する）により行った。測定方法は、一定視野（×１００）で同一試料内をランダムに５個所選び、定量分析を行い、平均値を測定値とした。Ｃｓの濃度はＦｅの濃度で規格化し、各試料の焼成前の濃度を１００％として算出した。 Furthermore, composition analysis and element mapping of the surface of the solidified product after firing were performed with a scanning electron microscope JSM-6010LA (hereinafter abbreviated as SEM-EDX) manufactured by JEOL Ltd. As a measuring method, five points in the same sample were randomly selected in a fixed visual field (× 100), quantitative analysis was performed, and an average value was used as a measured value. The Cs concentration was normalized by the Fe concentration, and the concentration before firing of each sample was calculated as 100%.
図３は、ＳＥＭ−ＥＤＸによる定量分析で、焼成前後の存在量の差から焼成後の固化物表面のＣｓ残存量を求めた特性図である。
この定量分析の結果、Ｃｓ残存量（率）がＯＰＣ固化物では約８４％であるのに対して、ＧＰ固化物のＧＰ／０．６では９９．２％、ＧＰ／０．９では９８．７％の高いＣｓ残存量であった。
FIG. 3 is a characteristic diagram in which the amount of Cs remaining on the surface of the solidified product after firing is obtained from the difference in the amount existing before and after firing by quantitative analysis using SEM-EDX.
As a result of this quantitative analysis, the Cs residual amount (rate) is about 84% for the OPC solidified product, whereas it is 99.2% for GP / 0.6 of the GP solidified product and 98.000 for GP / 0.9. The residual amount of Cs was as high as 7%.
図４はＧＰ固化物（ＧＰ／０．９）、図５はＯＰＣ固化物の焼成前後のＦｅならびにＣｓの分布の変化を示すＳＥＭ−ＥＤＸ写真である。両図とも（ａ）は焼成前のＦｅ、（ｂ）は焼成（５００℃、３時間）後のＦｅ、（ｃ）は焼成前のＣｓ、（ｄ）は焼成後のＣｓの分布を示している。両図において、白い点がＦｅあるいはＣｓを示している。 FIG. 4 is a SEM-EDX photograph showing changes in the distribution of Fe and Cs before and after firing the GP solidified product (GP / 0.9), and FIG. 5. In both figures, (a) is Fe before firing, (b) is Fe after firing (500 ° C., 3 hours), (c) is Cs before firing, and (d) is the distribution of Cs after firing. Yes. In both figures, white dots indicate Fe or Cs.
この元素マッピングの結果、ＧＰ固化物（ＧＰ／０．９）およびＯＰＣ固化物の何れも焼成前にＣｓがフェロシアン化物由来と思われるＦｅとほぼ同位置に存在していたのに対し、焼成後のＣｓはＦｅの位置とは関係なく固化物全体に分散していた。このことから、フェロシアン化物の分解によって、固定化されていたＣｓが一度移動できる形態に変化したと考えられる。 As a result of this elemental mapping, both the GP solidified product (GP / 0.9) and the OPC solidified product had Cs present at almost the same position as Fe, which seems to be derived from ferrocyanide, before firing. The latter Cs was dispersed throughout the solidified matter regardless of the position of Fe. From this, it is considered that the immobilized Cs changed to a form in which it could move once by the decomposition of the ferrocyanide.
さらに、焼成物について浸出（溶出）試験を行い、Ｃｓの浸出率を測定した。この浸出試験は、ＪＩＳ規格（ＪＩＳ Ｋ ００５８−１）に基づいて行った。
浸出試験の手順は、焼成物を２．０ｍｍ以下の大きさに粉砕し、篩分けして、固液比が１０（ｍｌ／ｇ）となるように粉砕試料に蒸留水を添加し、回転数２００ｒｐｍ，振幅４ｃｍ，２５℃の条件で６時間振とうを行う。
Further, a leaching (elution) test was performed on the fired product, and the leaching rate of Cs was measured. This leaching test was performed based on the JIS standard (JIS K 0058-1).
The procedure of the leaching test is to pulverize the fired product to a size of 2.0 mm or less, sieve, add distilled water to the pulverized sample so that the solid-liquid ratio is 10 (ml / g), and Shake for 6 hours under the conditions of 200 rpm, amplitude 4 cm, and 25 ° C.
その後、浸出液を３０００ｒｐｍで２０分間遠心分離し、上澄みを０．４５μｍのメンブレンフィルターでろ過した後、１Ｍ硝酸となるように調整し、株式会社日立ハイテクノロジー製 日立偏光ゼーマン原子吸光光度計 Ｚ−２０１０による測定を行う。 Thereafter, the leachate was centrifuged at 3000 rpm for 20 minutes, the supernatant was filtered through a 0.45 μm membrane filter, adjusted to 1 M nitric acid, and Hitachi Polarized Zeeman atomic absorption photometer Z-2010 manufactured by Hitachi High-Technology Corporation. Measure by.
図６は、この焼成物におけるＣｓの浸出率を示す特性図である。この図６に示すように、ＯＰＣ固化物では焼成物中のほぼ全てのセシウムが溶出したのに対し、ＧＰ固化物ではＣｓの溶出率はＧＰ／０．６で５．０％、ＧＰ／０．９で２．２％と低く抑えられた。なお、ＯＰＣ固化物の浸出率は１０６．５％となっているが、これは誤差値を含んでいるものと考えられる。 FIG. 6 is a characteristic diagram showing the leaching rate of Cs in the fired product. As shown in FIG. 6, in the OPC solidified product, almost all of the cesium in the fired product was eluted, whereas in the GP solidified product, the elution rate of Cs was 5.0% at GP / 0.6 and GP / 0. .9, it was kept low at 2.2%. The leaching rate of the OPC solidified product is 106.5%, which is considered to include an error value.
このことから、セメントでは、焼成後に固化物中に溜まったＣｓが水に可溶な状態で存在しているのに対して、ジオポリマーでは固化物中で不溶化（固定化）していると考えられる。また、Ｎａイオンの比率が大きいほど、すなわちＮａ２Ｏ／Ａｌ２Ｏ３のモル比の大きい方（ＧＰ／０．９）が、Ｃｓの溶出率が低かったことから、ゼオライトにおけるＣｓイオンの吸着機構と同様に、Ｃｓがジオポリマー構造中のＮａイオンと置換することで固定化されていると考えられる。 From this, in cement, Cs accumulated in the solidified product after firing exists in a state soluble in water, whereas in geopolymer, it is considered insolubilized (immobilized) in the solidified product. It is done. In addition, the larger the Na ion ratio, that is, the higher the molar ratio of Na 2 O / Al 2 O 3 (GP / 0.9), the lower the elution rate of Cs. Similar to the mechanism, it is considered that Cs is immobilized by substituting Na ions in the geopolymer structure.
以上の結果から、ジオポリマーとＣｓを吸着したフェロシアン化物を混合して焼成することで、フェロシアン化物を分解し、かつ、遊離したＣｓをジオポリマー中で固定化することができた。 From the above results, it was possible to decompose the ferrocyanide and fix the liberated Cs in the geopolymer by mixing and firing the geopolymer and the ferrocyanide adsorbing Cs.
なお、前記特許文献４には、都市ごみ焼却飛灰中のセシウムをジオポリマーで不溶化処理する発明が開示されている。しかし、この特許文献４に開示されている発明は、本発明のように、セシウムを吸着したフェロシアン化物とジオポリマーを混合して成形し、この成形物をフェロシアン化物の分解温度以上で焼成することにより、フェロシアン化物を分解し、かつフェロシアン化物から遊離したセシウムを焼成物内で固定化するフェロシアン化物に吸着した放射性セシウムの安定化処理方法ではない。 Patent Document 4 discloses an invention in which cesium in municipal waste incineration fly ash is insolubilized with a geopolymer. However, in the invention disclosed in Patent Document 4, as in the present invention, a ferrocyanide adsorbed with cesium and a geopolymer are mixed and molded, and the molded product is calcined at a decomposition temperature or higher of the ferrocyanide. Thus, it is not a method for stabilizing radioactive cesium adsorbed on ferrocyanide, in which ferrocyanide is decomposed and cesium released from ferrocyanide is immobilized in the fired product.
前記実施例ではフェロシアン化物として、硫酸ニッケルとフェロシアン化カリウムより生成されたフェロシアン化ニッケルを使用したが、本発明はこれに限定されるものではなく、例えばフェロシアン化鉄やフェロシアン化コバルトなど他のフェロシアン化遷移金属を用いることも可能である。 In the above embodiment, nickel ferrocyanide produced from nickel sulfate and potassium ferrocyanide was used as the ferrocyanide, but the present invention is not limited to this. For example, iron ferrocyanide, cobalt ferrocyanide, etc. It is also possible to use other ferrocyanide transition metals.
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