JP6014334B2 - Cesium transfer inhibitor - Google Patents

Description

  The present invention relates to a material for suppressing the movement of radioactive cesium in soil and a movement suppressing method using the material.

  There are many radioactive materials that are emitted in accidents at nuclear power plants and the like, but Cs137 has a long half-life and is a major component of radioactive materials. Moreover, about the field contaminated with the radioactive substance, if it moves to the crop produced from here, the problem of food contamination will arise. Furthermore, it is desired that the soil and incinerated ash contaminated with Cs137 at a high concentration do not move due to contact with water during storage.

  Since cesium is an alkali metal, it has high water solubility, and there are few or expensive chemicals that insolubilize it. Currently known cesium adsorbents include iron cyano complexes such as ferrocyanate and zeolites, but if the soil to be treated is enormous, it may be difficult to obtain, I am worried about the stability in the soil.

JP 2000-512759 A JP 2001-133594 A JP-A-5-254828 JP 2009-294017 A JP 2009-285635 A

Patent Document 1 discloses the use of a transition element hexacyanoferrate. The ion exchange of cesium using hexacyanoferrate is expressed by the following formula. _{A x M y [MFe (CN} ) 6] + 2Cs ⇔ Cs 2 [MFe (CN) 6] + xA + + yM 2+ ( wherein, x + y / 2 = 2 )

  Patent Document 2 discloses that, on the upstream side of the ion-exchange resin tower for desalting provided in the purification line for reactor cooling water, the adsorbent capable of selectively adsorbing cations such as cesium contained in the cooling water is radioactive. It discloses the adsorption and removal of nuclides and the use of titanate, hydrous titanium oxide or ferrocyanide as the adsorbent.

  In Patent Document 3, an adsorbent comprising an insoluble ferrocyanide is brought into contact with an aqueous cesium-containing solution in an adsorption step to adsorb cesium, and the insoluble ferrocyanide adsorbed in the desorption step is converted to an oxidizing desorbent solution. A method for recovering cesium is disclosed in which cesium is desorbed and recovered by contact to change to insoluble ferricyanide, and the resulting insoluble ferricyanide is converted to insoluble ferrocyanide by contacting with the regenerant solution.

  Although the said patent document 1 uses the hexacyano ferrate of a transition element as a ferrocyanide, if the ferrocyanide salt like potassium ferrocyanide or sodium which is easy to obtain as a general reagent etc. can be used, it is desirable. That is. However, such ferrocyanide salts have poor ability to adsorb or precipitate cesium or to separate it.

  Patent Document 4 introduces that there is a cement solidification method of incinerated ash as a method for treating radioactive substances, but if the incinerated ash contains an alkali, the solidified body will be expanded and destroyed. Teach you to blend.

  Although Patent Document 5 teaches the use of calcium silicate hydrate for wastewater treatment containing phosphorus, there is no suggestion that this is useful for adsorption and solidification of alkali ions such as cesium.

  The present invention provides a cesium migration inhibitor capable of easily adsorbing or precipitating cesium in contaminated soil using an easily available material and suppressing the migration thereof, and a migration inhibition method.

  The present inventor has been able to effectively suppress the movement of cesium in the soil, and as a result of various studies on a large amount of the inhibitor that can be obtained in large quantities, generally available active porous calcium silicate mineral is effective. As a result, the present invention has been completed.

  The present invention is a cesium migration inhibitor characterized by containing an active porous calcium silicate mineral as an active ingredient.

  Examples of the active porous calcium silicate mineral include one or more selected from tobermorite, zonotlite, and calcium silicate hydrate (CSH gel).

  Moreover, in addition to the said active porous calcium silicate mineral, it is a cesium movement inhibitor characterized by mix | blending zeolite as an active ingredient. Here, as the zeolite, zeolite mainly containing mordenite and / or chabazite is suitable.

  Moreover, in addition to the said active porous calcium silicate mineral, a zeolite, or both, it is the cesium movement inhibitor characterized by mix | blending active silicate glass powder as an active ingredient. Here, as the active silicate glass powder, one containing one or more selected from obsidian, pearlite, and potassium silicate fertilizer as a main component can be mentioned.

  Moreover, this invention is a cesium movement suppression method in soil characterized by mixing said cesium movement inhibitor in soil.

  Since the cesium movement inhibitor of the present invention contains active porous calcium silicate mineral as an active ingredient, it is easily available and has a high cesium movement inhibitory effect. Therefore, even if the soil is slightly contaminated with radioactive cesium, it is possible to cultivate crops, and it is possible to suppress the outflow of radioactive cesium from soil or waste containing radioactive cesium at a high concentration.

  The cesium migration inhibitor must have a function of solidifying or insolubilizing cesium ions by adsorption or precipitation. Active porous calcium silicate minerals have been found to have such a function.

  As the active porous calcium silicate mineral, tobermorite, zonotrite or calcium silicate hydrate (CSH gel) is suitable. However, any porous porous silicate mineral may be used as long as it is porous and mainly composed of calcium silicate. However, it is desirable that the mineral has water of crystallization or water of hydration. Here, “activity” means that many of the porous pores are fresh, and it is sufficient that they are extracted as minerals or synthesized. Those left for several years or in contact with high-concentration pollutants have low activity because the active sites are lost. However, even if it is such, it can be said that it is active since it becomes an active point if a new hole appears by crushing it. The degree of porosity can be defined by the bulk specific gravity. Assuming that the specific gravity of the non-porous calcium silicate mineral is 2.0 to 2.3, one having a range of 0.7 to 1.0 is suitable. This bulk specific gravity can be determined by taking a 100-200 mesh range of calcium silicate mineral, filling it into a graduated cylinder, and measuring or calculating this by a standard method. The porosity is preferably 50 to 90%. The active porous calcium silicate mineral is preferably used as a powder, and the particle size may be 0.05 to 10 mm, preferably 0.1 to 7 mm, more preferably 0.1 to 5 mm. The particle size is 10 mm or less, preferably 1 mm or less. Moreover, as an average diameter (Median diameter), about 100-1000 micrometers is preferable. And it is more preferable that 90 weight% or more of the whole exists in the said range.

  The active porous calcium silicate mineral can be a calcium silicate hydrate (CSH gel) which is a synthetic product, a silica plate or the like used for building materials. Examples of the calcium silicates include hydrates or molded products obtained by adding metal aluminum powder as a foaming agent to a slurry mainly composed of a siliceous raw material and a calcareous raw material, and hydrothermally reacting in an autoclave. The porosity is preferably 50 to 90%. In addition, lightweight cellular concrete boards and crushed calcium silicate boards can be used. Preferably, it is tobermorite, zonotrite or CSH gel, and those containing these as main components are preferred. Here, containing as a main component is 50 wt% or more, preferably 70 wt% or more.

  Moreover, since the calcium silicate board or lightweight cellular concrete board used as a building material is generated in large quantities at the time of demolition work or the like, it is more advantageous if it can be used effectively. The surface of calcium silicate board and lightweight cellular concrete board used in buildings is not active, but when this is pulverized, an active surface appears and becomes active porous calcium silicate particles.

  The active porous calcium silicate mineral is not particularly limited as long as it has an adsorption power for cesium, but is preferably porous and highly reactive with acid. Crystalline natural wollastonite (wollastonite) with low reactivity with acid and low activity, cement, mortar, blast furnace slag, non-ferrous metal slag, fly ash, concrete crushed materials, etc. have low cesium adsorption rate Therefore, it is not used.

The active porous calcium silicate mineral is excellent as a cesium migration inhibitor, but the effect as a migration inhibitor is improved by using it together with zeolite known as a cesium ion adsorbent. Zeolite is known to have various minerals, and any of them can be used. However, zeolite mainly composed of mordenite and / or chabasite has a more excellent function as a cesium transfer inhibitor. Zeolite is also preferably used as a powder in the same manner as the active porous calcium silicate mineral, and the preferred particle size is also the same.
When the active porous calcium silicate mineral and zeolite are used in combination, the ratio is preferably in the range of active porous calcium silicate mineral: zeolite (weight ratio) = 9: 1 to 3: 7.

Similarly to zeolite, active silicate glass powder can be blended as an active ingredient. Active silicate glass powders include, but are not limited to obsidian, perlite, or potassium silicate fertilizer. Here, the meaning of activity is the same as that described for the active porous calcium silicate mineral, and is preferably porous. The activated silicate glass powder is also preferably used as a powder in the same manner as the activated porous calcium silicate mineral and zeolite, and the preferred particle diameter is also the same.
The activated silicate glass powder can be used alone or in combination with zeolite and mixed with the activated porous calcium silicate mineral.

  When the active porous calcium silicate mineral and the active silicate glass powder are used in combination, the ratio is in the range of active porous calcium silicate mineral: active silicate glass powder (weight ratio) = 9: 1 to 5: 5 Is preferred. When the active porous calcium silicate mineral is used in combination with zeolite and active silicate glass powder, the ratio is the sum of the active porous calcium silicate mineral, zeolite and active silicate glass powder (weight ratio) = 9 : The range of 1-3: 7 is preferable. The ratio (weight ratio) of the zeolite and the active silicate glass powder is preferably in the range of 1: 9 to 9: 1.

  Without using an active porous calcium silicate mineral, it is also possible to combine a zeolite and an active silicate glass powder to form a cesium migration inhibitor. In this case, the ratio (weight ratio) of the zeolite and the active silicate glass powder is preferably in the range of 2: 8 to 8: 2.

The cesium migration inhibitor of the present invention is used by mixing with soil contaminated with radioactive cesium. The mixing ratio with respect to the soil varies depending on the degree of soil contamination, but for soil such as cultivated land where only the surface layer of the soil (depth of about 10 cm) is slightly contaminated, about 0.1 to 10 kg / m ² Suitable. When storing highly contaminated soil and incinerated ash together, about 0.1 to 10 kg / t is appropriate so that it will not diffuse into the ground or surroundings due to rainwater. For soil, once the cesium migration inhibitor is mixed in the above amount and mixed, no additional addition is required for several years or more unless new radioactive cesium is deposited. Depending on the crop, etc. on the ground, it may be absorbed as a part of the fertilizer component, so it is better to add it instead of the fertilizer. When plants such as crops are not cultivated, it is expected that the soil can be made semi-permanently safe.

  Since the cesium transfer inhibitor of the present invention has a high selective adsorption ability of cesium, the effect is large even in a small amount. Moreover, since bulk specific gravity is small, there exists an advantage that it is easy to work, such as mixing with soil easily. Moreover, since the cesium movement inhibitor of this invention can be used in a weak acidic-alkaline area | region, there are few restrictions with respect to use soil. Moreover, since the active porous calcium silicate mineral and potassium silicate fertilizer used in the cesium migration inhibitor of the present invention are also used as agricultural soil improvement materials or fertilizers, the effect as a fertilizer is also expected. The Therefore, the effect of making fertile farmland is expected without reducing the productivity of farmland.

Next, the present invention will be described in more detail with reference to examples. In addition, the cesium concentration in each example was performed using the atomic absorption photometry. It is understood that Example 1 is a reference example.

Example 1
As a model contamination solution, an aqueous solution to which a commercially available cesium chloride reagent was added so as to have a cesium concentration of 8.0 mg / l was prepared.
In 100 ml of this aqueous solution, 1 g of a commercially available calcium silicate fertilizer (manufactured by Kryon Co., Ltd.) was added as an active calcium silicate mineral, and the mixture was stirred at 25 ° C. for 6 hours and brought into contact. Thereafter, the aqueous solution was filtered with 5A filter paper, and the cesium concentration in the filtrate was measured. Table 1 shows the results of calculating the cesium adsorption rate and the cesium adsorption amount at this time.

Example 2
In 100 ml of the same aqueous solution used in Example 1, 5 parts by weight of the same active calcium silicate mineral as used in Example 1, and a commercially available mordenite-based zeolite soil improvement material (manufactured by New Tohoku Chemical Co., Ltd.) 1 g of a migration inhibitor prepared by mixing 5 parts by weight with a super mixer for 30 seconds was added, and the mixture was stirred and contacted at 25 ° C. for 6 hours in the same manner as in Example 1. Thereafter, the aqueous solution was filtered, and the cesium concentration in the filtrate was measured. Table 1 shows the results of calculating the cesium adsorption rate and the cesium adsorption amount at this time. The cesium adsorption coefficient at this time was 7.8 × 10 ³ mL / g.

Example 3
In 100 ml of the same aqueous solution used in Example 1, 10 parts by weight of the same active calcium silicate mineral as used in Example 1 and 1 part by weight of the same zeolite as used in Example 2 were mixed in a super mixer for 30 seconds. 1 g of the migration inhibitor prepared in this manner was added, and the mixture was stirred and contacted at 25 ° C. for 6 hours in the same manner as in Example 1. Thereafter, the aqueous solution was filtered, and the cesium concentration in the filtrate was measured. Table 1 shows the results of calculating the cesium adsorption rate and the cesium adsorption amount at this time.

Example 4
In 100 ml of the same aqueous solution used in Example 1, 7 parts by weight of the same active calcium silicate mineral as used in Example 1, and clinoptlite zeolite powder as a zeolite (produced in Nishiaizu, Fukushima Prefecture, 100-300 mesh powder) ) 1 g of a migration inhibitor prepared by mixing 3 parts by weight with a super mixer for 30 seconds was added, and the mixture was stirred and contacted at 25 ° C. for 6 hours in the same manner as in Example 1. Thereafter, the aqueous solution was filtered, and the cesium concentration in the filtrate was measured. Table 1 shows the results of calculating the cesium adsorption rate and the cesium adsorption amount at this time.

Example 5
In 100 ml of the same aqueous solution used in Example 1, 5 parts by weight of the same active calcium silicate mineral as used in Example 1, 2 parts by weight of the same zeolite mineral as used in Example 2, and activated silicate glass powder 1 g of a migration inhibitor prepared by mixing 3 parts by weight of obsidian powder (Sakai Parlato Kogyo Co., Ltd., 100-300 mesh powder) with a super mixer for 30 seconds and adding the same in the same manner as in Example 1 at 25 ° C. Stir for 6 h and contact. Thereafter, the aqueous solution was filtered, and the cesium concentration in the filtrate was measured. Table 1 shows the results of calculating the cesium adsorption rate and the cesium adsorption amount at this time.

Comparative Example 1
In 100 ml of the same aqueous solution used in Example 1, 1 g of commercially available wollastonite powder (TDI Corporation, 100-300 mesh powder) was added and stirred at 25 ° C. for 6 h in the same manner as in Example 1. Made contact. Thereafter, the aqueous solution was filtered, and the cesium concentration in the filtrate was measured. Table 2 shows the results of calculating the cesium adsorption rate and the cesium adsorption amount at this time.

Comparative Example 2
1 g of commercially available blast furnace slag powder (Nitetsu Blast Furnace Cement Co., Ltd., 100-300 mesh powder) is added to 100 ml of the same aqueous solution used in Example 1, and stirred at 25 ° C. for 6 hours in the same manner as in Example 1. And contacted. Thereafter, the aqueous solution was filtered, and the cesium concentration in the filtrate was measured. Table 2 shows the results of calculating the cesium adsorption rate and the cesium adsorption amount at this time.

Comparative Example 3
In 100 ml of the same aqueous solution used in Example 1, 1 g of commercially available steelmaking slag powder (Kusano Sangyo Co., Ltd., 100-300 mesh powder) was added and stirred at 25 ° C. for 6 hours in the same manner as in Example 1. Made contact. Thereafter, the aqueous solution was filtered, and the cesium concentration in the filtrate was measured. Table 2 shows the results of calculating the cesium adsorption rate and the cesium adsorption amount at this time.

Comparative Example 4
In 100 ml of the same aqueous solution used in Example 1, 1 g of 100-300 mesh crushed powder of potassium borosilicate (heat-resistant glass) was added, and the mixture was stirred and contacted at 25 ° C. for 6 hours in the same manner as in Example 1. It was. Thereafter, the aqueous solution was filtered, and the cesium concentration in the filtrate was measured. Table 2 shows the results of calculating the cesium adsorption rate and the cesium adsorption amount at this time.

Comparative Example 5
The same method as in Example 1 was added to 100 ml of the same aqueous solution used in Example 1, and 1 g of the same clinoptlite zeolite powder (produced in Nishiaizu, Fukushima Prefecture, 100-300 mesh powder) as used in Example 4 was added. And stirred at 25 ° C. for 6 h. Thereafter, the aqueous solution was filtered, and the cesium concentration in the filtrate was measured. Table 2 shows the results of calculating the cesium adsorption rate and the cesium adsorption amount at this time.

Comparative Example 6
To 100 ml of the same aqueous solution used in Example 1, 1 g of the same obsidian powder as used in Example 5 was added, and the mixture was stirred and contacted at 25 ° C. for 6 hours in the same manner as in Example 1. Thereafter, the aqueous solution was filtered, and the cesium concentration in the filtrate was measured. Table 2 shows the results of calculating the cesium adsorption rate and the cesium adsorption amount at this time.

Example 6
As model-contaminated soil, 100 g of sandy soil (West Japan Mining Co., Ltd .: No. 1 silica sand) previously dried for 24 hours at 100 ° C. is adjusted using a commercially available cesium chloride reagent so that the cesium concentration is 56.0 mg / l. 20 ml of the prepared aqueous solution was added and mixed to prepare artificially contaminated soil with a cesium content per 100 g of 0.933 mg.
In a 300 ml sealed container, 100 g of this artificially contaminated soil, 100 ml of pure water, and 1 g of the same migration inhibitor as used in Example 1 were shaken at 25 ° C. for 24 hours and brought into contact. Thereafter, the solution was extracted, and the cesium concentration in the filtrate was measured. Table 3 shows the cesium concentration in the solution at this time. At this time, the amount of cesium contained in 100 g of artificially contaminated soil was 0.933 mg, and the amount of cesium transferred into 100 ml of added water was 0.0 mg. Therefore, the transfer rate from the contaminated soil to the solution was 0%. It was.

Example 7
As model contaminated soil, 20 ml of aqueous solution adjusted to a cesium concentration of 56.0 mg / l using commercially available cesium chloride reagent is added to 100 g of sandy soil (Toyoura standard sand) previously dried at 100 ° C for 24 hours.・ Mixed to create artificially contaminated soil with a cesium content per 100g of 0.933mg.
In a 300 ml sealed container, 100 g of this artificially contaminated soil, 100 ml of pure water, and 1 g of the same migration inhibitor as used in Example 1 were shaken at 25 ° C. for 24 hours and brought into contact. Thereafter, the solution was extracted, and the cesium concentration in the filtrate was measured. Table 3 shows the cesium concentration in the solution at this time. At this time, the amount of cesium contained in 100 g of artificially contaminated soil was 0.933 mg, and the amount of cesium transferred into 100 ml of added water was 0.0 mg. Therefore, the transfer rate from the contaminated soil to the solution was 0%. It was.

Comparative Example 7
The same artificial contaminated soil as used in Example 6 was prepared. In a 300 ml sealed container, 100 g of this artificially contaminated soil and 100 ml of pure water were placed, and the whole container was shaken at 25 ° C. for 24 hours and brought into contact. Thereafter, the solution in the container was extracted, and the cesium concentration in the filtrate was measured. Table 3 shows the cesium concentration in the solution at this time.
At this time, the amount of cesium contained in 100 g of artificially contaminated soil was 0.933 mg, and the amount of cesium transferred into 100 ml of added water was 0.67 mg. Therefore, the transfer rate from the contaminated soil to the solution was 71.8%. It was.

Comparative Example 8
The same artificial contaminated soil as used in Example 7 was prepared. In a 300 ml sealed container, 100 g of this artificially contaminated soil and 100 ml of pure water were placed, and the whole container was shaken at 25 ° C. for 24 hours and brought into contact. Thereafter, the solution in the container was extracted, and the cesium concentration in the filtrate was measured. Table 3 shows the cesium concentration in the solution at this time.
At this time, the amount of cesium contained in 100 g of artificially contaminated soil was 0.933 mg, and the amount of cesium transferred into 100 ml of added water was 0.47 mg, so the transfer rate from contaminated soil to solution was 50.4%. It was.

Claims (4)

A powder mixture containing an active porous calcium silicate mineral powder having an average particle size (median diameter) of 100 to 1000 μm and a zeolite powder, wherein the active porous calcium silicate mineral: zeolite (weight ratio) = 9: 1 to A hydrate having a porosity of 50 to 90% obtained by hydrothermal reaction of a slurry containing an active porous calcium silicate mineral containing a siliceous raw material, a calcareous raw material, and metal aluminum powder in an autoclave. Alternatively, it is obtained by pulverizing a molded product, and the zeolite is a mordenite, chabazite or clinoptrite zeolite, and contains active porous calcium silicate mineral and zeolite as active ingredients. Cesium transfer inhibitor.   2. The cesium migration inhibitor according to claim 1, wherein the zeolite is mainly composed of mordenite. Further, obsidian having an average particle diameter (median diameter) of 100 to 1000 μm is blended as the active silicate glass powder, and the total of active porous calcium silicate mineral: zeolite and active silicate glass powder (weight ratio) = 9: The cesium migration inhibitor according to claim 1 or 2, wherein the ratio is 1 to 3: 7, and the ratio (weight ratio) of zeolite: active silicate glass powder is 1: 9 to 9: 1. A method for inhibiting cesium migration in soil, comprising mixing the cesium migration inhibitor according to any one of claims 1 to 3 into soil.