JP2013050313A - Method of desorbing cesium from soil - Google Patents
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- 239000002689 soil Substances 0.000 title claims abstract description 76
- 229910052792 caesium Inorganic materials 0.000 title claims abstract description 58
- TVFDJXOCXUVLDH-UHFFFAOYSA-N caesium atom Chemical compound [Cs] TVFDJXOCXUVLDH-UHFFFAOYSA-N 0.000 title claims abstract description 43
- 238000000034 method Methods 0.000 title claims abstract description 32
- 239000002253 acid Substances 0.000 claims abstract description 73
- DCYOBGZUOMKFPA-UHFFFAOYSA-N iron(2+);iron(3+);octadecacyanide Chemical compound [Fe+2].[Fe+2].[Fe+2].[Fe+3].[Fe+3].[Fe+3].[Fe+3].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-] DCYOBGZUOMKFPA-UHFFFAOYSA-N 0.000 claims abstract description 13
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims abstract description 11
- 229910017604 nitric acid Inorganic materials 0.000 claims abstract description 11
- 239000007864 aqueous solution Substances 0.000 claims description 48
- 239000003463 adsorbent Substances 0.000 claims description 24
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 10
- 229960003351 prussian blue Drugs 0.000 claims description 10
- 239000013225 prussian blue Substances 0.000 claims description 10
- 238000003795 desorption Methods 0.000 claims description 7
- 238000009835 boiling Methods 0.000 claims description 4
- 239000000126 substance Substances 0.000 claims description 4
- 230000018044 dehydration Effects 0.000 claims 1
- 238000006297 dehydration reaction Methods 0.000 claims 1
- 238000000926 separation method Methods 0.000 claims 1
- -1 cesium ions Chemical class 0.000 abstract description 22
- 239000007788 liquid Substances 0.000 abstract description 18
- 238000000605 extraction Methods 0.000 abstract description 11
- 239000002105 nanoparticle Substances 0.000 abstract description 7
- 239000000463 material Substances 0.000 description 9
- 239000000243 solution Substances 0.000 description 8
- 238000001179 sorption measurement Methods 0.000 description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 8
- 239000011260 aqueous acid Substances 0.000 description 7
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- NCMHKCKGHRPLCM-UHFFFAOYSA-N caesium(1+) Chemical compound [Cs+] NCMHKCKGHRPLCM-UHFFFAOYSA-N 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 238000011161 development Methods 0.000 description 3
- 238000002156 mixing Methods 0.000 description 3
- 238000012545 processing Methods 0.000 description 3
- 230000002285 radioactive effect Effects 0.000 description 3
- 239000002904 solvent Substances 0.000 description 3
- 239000002699 waste material Substances 0.000 description 3
- CPELXLSAUQHCOX-UHFFFAOYSA-N Hydrogen bromide Chemical compound Br CPELXLSAUQHCOX-UHFFFAOYSA-N 0.000 description 2
- 238000000354 decomposition reaction Methods 0.000 description 2
- 238000001962 electrophoresis Methods 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- VLTRZXGMWDSKGL-UHFFFAOYSA-N perchloric acid Chemical compound OCl(=O)(=O)=O VLTRZXGMWDSKGL-UHFFFAOYSA-N 0.000 description 2
- 239000012857 radioactive material Substances 0.000 description 2
- 239000002901 radioactive waste Substances 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- VWDWKYIASSYTQR-UHFFFAOYSA-N sodium nitrate Chemical compound [Na+].[O-][N+]([O-])=O VWDWKYIASSYTQR-UHFFFAOYSA-N 0.000 description 2
- 229910000851 Alloy steel Inorganic materials 0.000 description 1
- 239000004743 Polypropylene Substances 0.000 description 1
- 239000004809 Teflon Substances 0.000 description 1
- 229920006362 Teflon® Polymers 0.000 description 1
- 229910021536 Zeolite Inorganic materials 0.000 description 1
- 150000007513 acids Chemical class 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- QZPSXPBJTPJTSZ-UHFFFAOYSA-N aqua regia Chemical compound Cl.O[N+]([O-])=O QZPSXPBJTPJTSZ-UHFFFAOYSA-N 0.000 description 1
- 239000011230 binding agent Substances 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- TVFDJXOCXUVLDH-OUBTZVSYSA-N cesium-134 Chemical compound [134Cs] TVFDJXOCXUVLDH-OUBTZVSYSA-N 0.000 description 1
- TVFDJXOCXUVLDH-RNFDNDRNSA-N cesium-137 Chemical compound [137Cs] TVFDJXOCXUVLDH-RNFDNDRNSA-N 0.000 description 1
- 239000002734 clay mineral Substances 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 238000005202 decontamination Methods 0.000 description 1
- 230000003588 decontaminative effect Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 239000007772 electrode material Substances 0.000 description 1
- 230000008030 elimination Effects 0.000 description 1
- 238000003379 elimination reaction Methods 0.000 description 1
- 238000010828 elution Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000011010 flushing procedure Methods 0.000 description 1
- 229910000042 hydrogen bromide Inorganic materials 0.000 description 1
- 239000002440 industrial waste Substances 0.000 description 1
- 229910052500 inorganic mineral Inorganic materials 0.000 description 1
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 239000010445 mica Substances 0.000 description 1
- 229910052618 mica group Inorganic materials 0.000 description 1
- 239000011707 mineral Substances 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- 238000012856 packing Methods 0.000 description 1
- 239000000049 pigment Substances 0.000 description 1
- 229920001155 polypropylene Polymers 0.000 description 1
- 229920000915 polyvinyl chloride Polymers 0.000 description 1
- 239000004800 polyvinyl chloride Substances 0.000 description 1
- 238000005067 remediation Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 239000010802 sludge Substances 0.000 description 1
- 239000000264 sodium ferrocyanide Substances 0.000 description 1
- GTSHREYGKSITGK-UHFFFAOYSA-N sodium ferrocyanide Chemical compound [Na+].[Na+].[Na+].[Na+].[Fe+2].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-] GTSHREYGKSITGK-UHFFFAOYSA-N 0.000 description 1
- 235000012247 sodium ferrocyanide Nutrition 0.000 description 1
- 235000010344 sodium nitrate Nutrition 0.000 description 1
- 239000004317 sodium nitrate Substances 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000004381 surface treatment Methods 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
- 239000010457 zeolite Substances 0.000 description 1
Landscapes
- Processing Of Solid Wastes (AREA)
- Water Treatment By Sorption (AREA)
- Solid-Sorbent Or Filter-Aiding Compositions (AREA)
Abstract
Description
本発明は、土壌からセシウムを脱離し必要により抽出する方法に関する。 The present invention relates to a method for detaching cesium from soil and extracting it if necessary.
原子力発電所の事故の際には、大量の放射性物質が環境に飛散することがある。中でも、放射性であるセシウム１３４とセシウム１３７は遠距離まで飛散することが知られており、その対策が大きな課題となる。実際、２０１１年３月に起こった福島第一原子力発電所の事故でも、ある程度距離が離れた地域では、ある程度時間が経った後に問題となっているのはこの二つの放射性物質だけである。
特に、農地や校庭、空き地などの土壌に落下した放射性セシウムは、粘土鉱物などの成分に強く吸着することが知られている。これらの対策としては、表層土を剥離し、客土を入れることなどが提案されている。しかしながら、このようにして生じる表層土は放射性廃棄物として取り扱う必要がある一方、その量は膨大となり、その処理法の検討が課題である。このような放射性廃棄物である土壌の処理法として、セシウムを土壌から抽出し、別の吸着材等に吸着させることで、その土自体を再利用可能もしくは一般の産業廃棄物としての処理を行うということが考えられる。現在知られている土壌からのセシウムの抽出法としては、電気泳動法を使用する方法（非特許文献１）、酸による洗浄（非特許文献２、特許文献１）が知られている。
In the event of a nuclear power plant accident, a large amount of radioactive material may be scattered into the environment. Among them, radioactive cesium 134 and cesium 137 are known to scatter to a long distance, and countermeasures thereof are a major issue. In fact, even in the accident at the Fukushima Daiichi nuclear power plant that occurred in March 2011, it is only these two radioactive materials that have become a problem after a certain amount of time in an area some distance away.
In particular, it is known that radioactive cesium that has fallen into soil such as farmland, schoolyards, and vacant land is strongly adsorbed by components such as clay minerals. As these measures, it has been proposed to peel off the surface soil and put in the soil. However, the surface soil thus generated needs to be handled as radioactive waste, but the amount of the soil becomes enormous, and examination of the treatment method is a problem. As a method for treating soil as such radioactive waste, cesium is extracted from the soil and adsorbed on another adsorbent, etc., so that the soil itself can be reused or treated as general industrial waste. It can be considered. Known methods for extracting cesium from soil include a method using electrophoresis (Non-Patent Document 1) and an acid wash (Non-Patent Document 2, Patent Document 1).
電気泳動を使用する方法は、土壌を電極間に配置し、電圧を印可しながら水または弱酸で洗浄する方法である。この場合、ほぼ全てのセシウムを抽出することが可能であるが、１５日など、長期の時間を要することが課題である。一方、酸による洗浄では、６モル／リットルなどの加熱した硝酸、王水、塩酸などの高濃度の酸の利用が報告されている。これらの場合も７０〜９５％程度のセシウムを抽出することが可能である。しかしながら、実用的には大量の土壌を処理するためには、加熱した高濃度の酸は、使用する容器などの課題がある。また、要する時間は報告によると１時間しんとう後、一晩静置であり、やはり時間を要する。また、特許文献１では、酸濃度を下げるために、土壌に対する酸水溶液の使用量を上げることが提案されている。この提案により、容器の選択性などの問題が解決される。しかしながら、水溶液の使用量を増加させることにより廃液量の増加が懸念される。 The method using electrophoresis is a method in which soil is placed between electrodes and washed with water or a weak acid while applying a voltage. In this case, it is possible to extract almost all of cesium, but it takes a long time such as 15 days. On the other hand, in acid cleaning, use of high-concentration acids such as heated nitric acid such as 6 mol / liter, aqua regia and hydrochloric acid has been reported. In these cases, it is possible to extract about 70 to 95% of cesium. However, practically, in order to treat a large amount of soil, heated high-concentration acid has problems such as a container to be used. According to the report, the time required is to stand still after one hour, and it still takes time. Moreover, in patent document 1, in order to reduce an acid concentration, raising the usage-amount of the acid aqueous solution with respect to soil is proposed. This proposal solves problems such as container selectivity. However, there is a concern about an increase in the amount of waste liquid by increasing the amount of aqueous solution used.
土壌からセシウムイオンを抽出する際に、高濃度の酸を使用することなく、土壌量に対する酸水溶液の量を低減し、作業により排出される廃液の量を減らすことを目的とする。
When extracting cesium ions from soil, the purpose is to reduce the amount of acid aqueous solution relative to the amount of soil and reduce the amount of waste liquid discharged by the work without using high-concentration acid.
前記の課題は下記の手段により解決された。
［１］ 酸水溶液を土壌及びセシウム吸着材に交互に接触させることで、効率的にセシウムを土壌から脱離させる方法。
［２］ 前記酸水溶液として、硝酸もしくは硫酸を使用する［１］に記載の脱離方法。
［３］ 前記酸水溶液と土壌の接触時の温度を９０℃以上とする［１］または［２］に記載の脱離方法。
［４］ 前記酸水溶液と土壌の接触時において、圧力容器及び／又は他の薬剤の添加による沸点上昇を利用することにより、１００℃を超える温度とする［１］〜［３］のいずれかに記載の脱離方法。
［５］ 前記セシウム吸着剤として、プルシアンブルーを用いる［１］〜［４］のいずれかに記載の脱離方法。
The above problems have been solved by the following means.
[1] A method of efficiently desorbing cesium from soil by bringing an acid aqueous solution into contact with soil and a cesium adsorbent alternately.
[2] The desorption method according to [1], wherein nitric acid or sulfuric acid is used as the acid aqueous solution.
[3] The desorption method according to [1] or [2], wherein the temperature at the time of contact between the acid aqueous solution and soil is 90 ° C. or higher.
[4] At the time of contact between the acid aqueous solution and the soil, by using a rise in boiling point due to the addition of a pressure vessel and / or other chemicals, a temperature exceeding 100 ° C. is used. Desorption method as described.
[5] The desorption method according to any one of [1] to [4], wherein Prussian blue is used as the cesium adsorbent.
本発明の方法によれば、低濃度の酸を使用するにあたり、土壌量に対する酸水溶液の量（以下固液比と呼ぶ）を低減した上で、高い固液比を使用した際と同様のセシウムの酸水溶液への抽出が可能となる。
この手法では、酸水溶液を土壌及びセシウム吸着材に交互に接触させることにより、土壌からの抽出により上がった酸水溶液中のセシウムイオン濃度を、吸着材との接触により低下させることが重要である。セシウムイオン濃度を低下させた酸水溶液を再度土壌に接触させることにより、土壌から酸水溶液へのセシウムイオンの抽出を加速させることができる。
According to the method of the present invention, when using a low concentration acid, the amount of the acid aqueous solution with respect to the soil amount (hereinafter referred to as the solid-liquid ratio) is reduced, and the same cesium as when using a high solid-liquid ratio Can be extracted into an aqueous acid solution.
In this method, it is important to reduce the concentration of cesium ions in the aqueous acid solution raised by extraction from the soil by contact with the adsorbent by alternately contacting the acid aqueous solution with the soil and the cesium adsorbent. Extraction of cesium ions from the soil to the acid aqueous solution can be accelerated by bringing the acid aqueous solution having a reduced cesium ion concentration into contact with the soil again.
本発明のセシウムの脱離方法においては、強酸水溶液を土壌土（本明細書では土壌の土を地層そのものと区別して土壌土もしくは土壌の土ということがある。）と、セシウム吸着材を交互に接触させる。強酸水溶液と土壌を接触させる方法としては特に問わないが、例えば土壌を酸水溶液に浸漬する方法、土壌をカラム上の物に詰め、酸水溶液を通水する方法、土壌に酸水溶液を散布する方法、酸水溶液を加熱水蒸気として土壌と接触させる方法などが上げられる。必要に応じて攪拌などの処理を行ってもよい。 In the method of desorbing cesium of the present invention, a strong acid aqueous solution is used as soil soil (in this specification, soil soil is sometimes referred to as soil soil or soil soil), and cesium adsorbent is alternately used. Make contact. The method of bringing the strong acid aqueous solution into contact with the soil is not particularly limited. For example, the method of immersing the soil in the acid aqueous solution, the method of packing the soil into a column and passing the acid aqueous solution, the method of spraying the acid aqueous solution on the soil And a method of bringing the acid aqueous solution into contact with the soil as heated steam. You may perform processes, such as stirring, as needed.
酸水溶液とセシウム吸着材の接触方法についても特に制限はなく、土壌と酸水溶液との接触方法と同様の手法を取ることができる。ただし、セシウム吸着材が液状もしくは液体に分散もしくは溶解するものであり、混合後に酸水溶液とセシウム吸着材が分離できるのであれば、単に混合するという手法も取ることができる。 There is no restriction | limiting in particular also about the contact method of acid aqueous solution and a cesium adsorption material, The method similar to the contact method of soil and acid aqueous solution can be taken. However, if the cesium adsorbent is liquid or is dispersed or dissolved in a liquid and the aqueous acid solution and the cesium adsorbent can be separated after mixing, a method of simply mixing can also be taken.
酸水溶液を土壌及びセシウム吸着材に接触させる回数については特に制限はない。また、酸水溶液を土壌に複数回接触させた後にセシウム吸着材に接触させるなど、交互に接触させるサイクル毎の接触回数、接触時間についても特に制限はない。（ここで、酸水溶液を土壌に接触させ、次にセシウム吸着材に接触させることを一サイクルとする。）ただし、本発明の目的が、一旦上昇した酸水溶液のセシウムイオン濃度を低下させ、再度土壌に接触させることであるため、土壌と酸水溶液の接触は少なくとも二サイクルは必要である。また、このサイクルを繰り返す際に、途中で酸水溶液を新しいものと交換してもよいが、この場合も、本発明の効果を得るためには、少なくとも一度は同一の酸水溶液で二サイクルを経る必要がある。 There is no particular limitation on the number of times the acid aqueous solution is brought into contact with the soil and the cesium adsorbent. Moreover, there is no restriction | limiting in particular also about the frequency | count of a contact for every cycle and contact time which are made to contact with a cesium adsorbent, after making an acid aqueous solution contact with soil several times. (Here, it is one cycle that the acid aqueous solution is brought into contact with the soil and then brought into contact with the cesium adsorbent.) However, the purpose of the present invention is to reduce the cesium ion concentration of the acid aqueous solution once increased, and again Since the contact is with the soil, the contact between the soil and the aqueous acid solution requires at least two cycles. In addition, when this cycle is repeated, the acid aqueous solution may be replaced with a new one in the middle. In this case, too, in order to obtain the effect of the present invention, at least once, the same acid aqueous solution is used for two cycles. There is a need.
土壌と酸水溶液を接触させる際の温度としては、６０℃以上が好ましく、９０℃以上がより好ましい。さらには、塩や溶媒などの他の薬剤を酸水溶液に添加することによる沸点上昇や、加熱時に圧力容器を利用するなどにより、１００℃以上に上昇させることができれば、セシウム抽出に関してはさらに有効である。さらには、加熱水蒸気の利用など、蒸気などを利用した高温処理も利用できる。この場合も、他の溶媒を、加熱のために併用することなどもできる。上限は特にないが、１２００℃以下であることが実際的である。セシウム吸着材と酸水溶液を接触させる際の温度には特に制限はなく、セシウム吸着材によるセシウム吸着が適切になされ、土壌及びセシウム吸着材が分解などの劣化が起こらなければよい。
固液比については、特に問わないが、セシウム抽出効率の観点からは高い方が望ましい。ただし、廃液量の制限の観点からは少ない方が望ましく、これらから総合的に決定されるべきものである。例えば、１：５から１：１００程度が使用できる。
As temperature at the time of making soil and acid aqueous solution contact, 60 degreeC or more is preferable and 90 degreeC or more is more preferable. Furthermore, if the temperature can be raised to 100 ° C. or higher by increasing the boiling point by adding other chemicals such as salts and solvents to the acid aqueous solution or using a pressure vessel during heating, it is more effective for cesium extraction. is there. Furthermore, high-temperature treatment using steam or the like such as heating steam can be used. In this case also, other solvents can be used in combination for heating. Although there is no upper limit in particular, it is practical that it is 1200 degrees C or less. There is no restriction | limiting in particular in the temperature at the time of making a cesium adsorbent and acid aqueous solution contact, The cesium adsorption by a cesium adsorbent is made appropriately, and degradation, such as decomposition | disassembly of a soil and a cesium adsorbent, does not occur.
The solid-liquid ratio is not particularly limited, but a higher one is desirable from the viewpoint of cesium extraction efficiency. However, a smaller amount is desirable from the viewpoint of limiting the amount of waste liquid, and should be determined comprehensively. For example, about 1: 5 to 1: 100 can be used.
使用する酸水溶液は、酸と水を含んでいればよく、それらが主たる構成物である必要もない。例えば沸点の制御のため、塩を添加することや、他の溶媒との混合液とすることなども効果的である。酸については、電離度の高い強酸であることが好ましい。具体的には、硫酸、硝酸、塩酸、過塩素酸、臭化水素などが好ましく、特に硫酸、硝酸が好ましい。中でも硫酸は電離することにより一分子あたり二つの水素イオンを供給できるため、特に効果的である。酸水溶液の濃度はセシウム脱離の効果としてはより濃度が高いことが望ましいが、実用性を考えると３モル／リットル以下とすることも可能である。また、１モル／リットル以下とすることも可能である。また、このように酸濃度を低くすることで、土壌への影響が低減され、アルミニウムイオン、鉄イオン、各種有機物由来の分解物などの水溶液への溶出を抑えることができる。これは、後述する水溶液からのセシウムイオンの回収時に効果を発揮する。また、酸濃度を低減することにより、土壌の劣化を低減させることができ、結果として処理後の土壌を再度採取した場所に復元することも可能となる。酸の濃度に下限値は特にないが、０.０１モル／リットル以上とすることが実際的である。 The acid aqueous solution to be used should just contain an acid and water, and does not need to be the main components. For example, in order to control the boiling point, it is also effective to add a salt or to make a mixed solution with another solvent. The acid is preferably a strong acid having a high degree of ionization. Specifically, sulfuric acid, nitric acid, hydrochloric acid, perchloric acid, hydrogen bromide and the like are preferable, and sulfuric acid and nitric acid are particularly preferable. Among them, sulfuric acid is particularly effective because it can supply two hydrogen ions per molecule by ionization. The concentration of the aqueous acid solution is desirably higher as the effect of cesium elimination, but can be 3 mol / liter or less in view of practicality. Moreover, it is also possible to set it as 1 mol / liter or less. Further, by lowering the acid concentration in this way, the influence on the soil is reduced, and elution into an aqueous solution of aluminum ions, iron ions, decomposition products derived from various organic substances, and the like can be suppressed. This is effective when recovering cesium ions from an aqueous solution described later. Further, by reducing the acid concentration, it is possible to reduce the deterioration of the soil, and as a result, it is possible to restore the treated soil to a location where it has been collected again. Although there is no particular lower limit to the acid concentration, it is practical to set the acid concentration to 0.01 mol / liter or more.
処理時間は特に制限されないが、本発明の好ましい実施形態によれば９６時間以内の処理でセシウムを十分に脱離することができる。下限値は特にないが１分以上が実際的である。また、酸濃度は常に一定である必要はなく、処理により酸濃度が低下した場合には、酸の追加などで適宜調整をおこなってもよい。 The treatment time is not particularly limited, but according to a preferred embodiment of the present invention, cesium can be sufficiently desorbed by treatment within 96 hours. Although there is no lower limit, 1 minute or more is practical. Further, the acid concentration does not always have to be constant, and when the acid concentration is reduced by the treatment, the acid concentration may be appropriately adjusted by adding an acid or the like.
セシウム吸着材及び使用する容器の種類に特に制限はないが、酸濃度を低減させることで、吸着材や、処理容器に要求される耐酸性が変わるため、本発明により、使用できる材料が広がる。この耐酸性を満たせば吸着材、処理容器共に特に制限はないが、例えば、吸着材としては、プルシアンブルーなどのフェロシアン化物、ゼオライト、パーミキュライト、雲母などの天然鉱物などが利用できる。なかでも、プルシアンブルーは、高いシウム吸着能力と共に、安価であること、金属置換により吸着能力をさらに改善できることなどの特徴を有するものである。 Although there is no restriction | limiting in particular in the kind of cesium adsorption material and the container to be used, Since the acid resistance requested | required of adsorption material and a processing container changes by reducing an acid concentration, the material which can be used spreads out by this invention. If the acid resistance is satisfied, both the adsorbent and the processing container are not particularly limited. For example, as the adsorbent, ferrocyanide such as Prussian blue, natural mineral such as zeolite, permiculite, mica, and the like can be used. Among them, Prussian blue has characteristics such as high adsorption capacity and low cost, and further improved adsorption capacity by metal substitution.
プルシアンブルーについては、顔料やセシウム吸着材としての用途だけでなく、エレクトロクロミック材料、センサ、二次電池電極材料等の機能性材料としての用途が知られているが、その中で、本発明者らは、プルシアンブルーやプルシアンブルー類似体のナノ粒子化と、それを利用した素子開発をすすめてきた（国際公開第２００８／０８１９２３号参照）。
本発明において、セシウム吸着剤として、従来のプルシアンブルーが好ましく用いられることは前述のとおりであるが、特に、プルシアンブルーのナノ粒子を用いた場合には、粒径が小さく、大きな比表面積を有するため、高い吸着効果を有するものであるので、セシウム吸着剤として特に好ましい。また、前記の国際公開第２００８／０８１９２３号に記載された方法で表面処理を施したものを用いた場合には、水に分散することが可能であるので、分散液として使用することができる。
Prussian blue is known not only as a pigment or cesium adsorbent, but also as a functional material such as an electrochromic material, a sensor, and a secondary battery electrode material. Have promoted the development of nanoparticles of Prussian blue and Prussian blue analogues and device development using the nanoparticles (see International Publication No. 2008/081923).
In the present invention, the conventional Prussian blue is preferably used as the cesium adsorbent as described above. Particularly, when Prussian blue nanoparticles are used, the particle size is small and the specific surface area is large. Therefore, since it has a high adsorption effect, it is particularly preferable as a cesium adsorbent. Moreover, when using what was surface-treated by the method described in the said international publication 2008/081923, since it can be disperse | distributed to water, it can be used as a dispersion liquid.
また、吸着材は、セシウム吸着能を持つもののみから成る必要はなく、バインダ、基材等との複合体であってもよい。処理容器としては、ステンレスなどの合金鋼材、ポリプロピレン、ポリ塩化ビニル、テフロン（登録商標）などの樹脂などで、使用する酸に対する適切な耐久性を持つものが使用できる。 Further, the adsorbent does not need to be composed only of a material having a cesium adsorption ability, and may be a composite with a binder, a base material, and the like. As the processing container, an alloy steel material such as stainless steel, a resin such as polypropylene, polyvinyl chloride, Teflon (registered trademark), or the like having a suitable durability against the acid used can be used.
温度、土壌及び酸水溶液の固液比、酸の種類が効果的な要素となる。温度を上昇させることにより、低濃度の酸水溶液によっても、より迅速にセシウムを土壌から脱離させることが可能となる。また、土壌に対する水溶液中の水素イオンの比を上げることにより、より迅速に多くのセシウムイオンを土壌から抽出することができる。このため、高濃度の酸を使用せずとも、土壌に対する酸水溶液の固液比を上げることにより、効率的なセシウムの抽出が可能となる。 The temperature, the solid-liquid ratio of the soil and the acid aqueous solution, and the type of acid are effective factors. By increasing the temperature, cesium can be more rapidly desorbed from the soil even with a low-concentration acid aqueous solution. Further, by increasing the ratio of hydrogen ions in the aqueous solution to the soil, more cesium ions can be extracted from the soil more quickly. For this reason, it is possible to efficiently extract cesium by increasing the solid-liquid ratio of the acid aqueous solution to the soil without using a high concentration acid.
セシウム抽出後の土壌は、適切な処理を追加することも可能であり、その内容に制限はない。例えば、土壌中酸濃度を下げるために、水洗、酸を含まない加熱水蒸気などを使用した処理などを行うことができる。廃棄することを目的として、加熱、焼却などの処理を行い、重量、体積を低減することもできる。 Appropriate treatment can be added to the soil after cesium extraction, and there is no restriction on the content. For example, in order to reduce the acid concentration in the soil, washing with water, treatment using heated steam not containing acid, or the like can be performed. For the purpose of disposal, treatment such as heating and incineration can be performed to reduce the weight and volume.
以下に、本発明を実施例に基づいてさらに詳細に説明するが、本発明はこれにより限定して解釈されるものではない。 Hereinafter, the present invention will be described in more detail based on examples, but the present invention should not be construed as being limited thereto.
（比較例）
土壌の土（福島県飯舘村、褐色森林土）と０.１ｇと、０.５モル／リットルの硝酸水溶液を混合、９５℃にて４５分静置後の硝酸水溶液に抽出されたセシウムイオン濃度と、固液比の関係を表１に示した。この通り、セシウム吸着材の接触を行わない場合には、土壌土から効率的にセシウムイオンを抽出させるには固液比を上げることが必要であり、例えば４０％以上の抽出率を達成するには、固液比を７５まで上げる必要がある。
(Comparative example)
Cesium ion concentration extracted from the soil (Iitate village, Fukushima Prefecture, brown forest soil), 0.1 g, and 0.5 mol / liter nitric acid aqueous solution, and left at 95 ° C for 45 minutes. Table 1 shows the relationship between the solid-liquid ratio. As described above, when the cesium adsorbent is not contacted, it is necessary to increase the solid-liquid ratio in order to efficiently extract cesium ions from the soil, and for example, to achieve an extraction rate of 40% or more. Needs to increase the solid-liquid ratio to 75.
（実施例）
本実施例では、セシウム吸着剤として、フェロシアン化ナトリウムの水溶液に硝酸鉄の水溶液を混合して析出させた、粒径２０ｎｍ以下のプルシアンブルーナノ粒子（前記国際公開第２００８／０８１９２３号の［００５８］参照）、すなわち、表面処理が施されていない水不溶性のプルシアンブルーナノ粒子を用いた。
前記比較例で使用したものと同種の土壌土５.７２９６ｇをカラムに充填し、０.５モル／リットルの硝酸水溶液１００ｍｌを通水した（固液比１７.５）。ところ、７時間の通水で３０.１％の土壌中のセシウムイオンが硝酸水溶液に抽出できた。さらに２時間（計９時間）通水したところ、抽出量は３０.４６％と７時間における値と比較してほぼ一定であった。ここで、酸水溶液を不溶性のプルシアンブルーナノ粒子を充填したカラムに二回通水したところ、１００％のセシウムイオンが酸水溶液から除去できた。この酸水溶液を使用し、再度土壌を充填したカラムに４時間通水したところ、酸水溶液に新たに１０.２％のセシウムイオンが酸水溶液に抽出された。よって、この二サイクルで土壌から計３９.６％のセシウムイオンが抽出された。このように、一度の通水で抽出量が一旦飽和した後であっても、酸水溶液中のセシウムイオンを除去することにより、さらに抽出量を増やすことが可能である。また、比較例に示すとおり、単なる土壌と酸水溶液の接触の場合、４０％の抽出の実現には固液比７５が必要であったが、一旦プルシアンブルーにより酸水溶液中のセシウムイオンを除去することにより、固液比１７.５で実現することができた。
(Example)
In this example, Prussian blue nanoparticles having a particle size of 20 nm or less (as described in International Publication No. 2008/081923 [0058], which were prepared by mixing an aqueous solution of sodium nitrate with an aqueous solution of sodium ferrocyanide as a cesium adsorbent. ], That is, water-insoluble Prussian blue nanoparticles not subjected to surface treatment were used.
The column was filled with 5.7296 g of the same soil as that used in the comparative example, and 100 ml of a 0.5 mol / liter nitric acid aqueous solution was passed through (solid-liquid ratio 17.5). However, 30.1% of the cesium ions in the soil could be extracted into the aqueous nitric acid solution by passing water for 7 hours. Further, when water was passed for 2 hours (9 hours in total), the extraction amount was 30.46%, which was almost constant compared to the value at 7 hours. Here, when the aqueous acid solution was passed twice through a column packed with insoluble Prussian blue nanoparticles, 100% of the cesium ions could be removed from the aqueous acid solution. When this acid aqueous solution was used and water was passed through a column filled with soil again for 4 hours, 10.2% cesium ions were newly extracted into the acid aqueous solution. Therefore, a total of 39.6% cesium ions were extracted from the soil in these two cycles. Thus, even after the extraction amount is once saturated by passing water once, it is possible to further increase the extraction amount by removing cesium ions in the acid aqueous solution. Further, as shown in the comparative example, in the case of simple contact between the soil and the acid aqueous solution, a solid-liquid ratio of 75 was necessary to realize 40% extraction, but once the cesium ions in the acid aqueous solution were removed by Prussian blue. As a result, a solid-liquid ratio of 17.5 could be realized.
放射性セシウムに汚染された土壌は、農地、校庭、空き地など、多様にわたる。本発明は、これらの除染に大きな効果を発揮すると期待される。また、汚泥やその焼却灰なども、各種土壌由来の酸化物にセシウムが吸着していると考えられ、同様の利用が可能である。 Soil contaminated with radioactive cesium is diverse, including farmland, schoolyards and vacant land. The present invention is expected to exert a great effect on these decontamination. In addition, sludge and its incinerated ash are considered to be adsorbed by various soil-derived oxides and can be used in the same manner.
Claims (5)
The desorption method according to any one of claims 1 to 4, wherein Prussian blue is used as the cesium adsorbent.
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| JP2014100700A (en) * | 2012-10-23 | 2014-06-05 | Okuto:Kk | Method for decontaminating contaminated soil |
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