JP6434108B2 - Radioactive cesium plant migration inhibitor, method for producing the same, and plant growth method - Google Patents

Description

  The present invention relates to a plant migration inhibitor of radioactive cesium, a production method thereof, and a plant growth method.

The scattering of radioactive materials caused by the accident at the TEPCO Fukushima Daiichi Nuclear Power Station following the Great East Japan Earthquake is not limited to the power plant, and it continues to detect radiation exceeding the standard value in a wide range of surrounding areas. In these areas, it is desired to provide a decontamination method for contaminated soil contaminated with radioactive substances and a method for suppressing the migration of radioactive substances from contaminated soil contaminated with radioactive substances to plants.
In particular, radioactive materials that cause problems in nuclear power plant accidents include cesium 134 (Cs134) and cesium 137 (Cs137) (hereinafter, cesium 134 and cesium 137 are collectively referred to as "radioactive cesium"). Among these, measures against cesium 137 (Cs137) having a long half-life of 30 years are required.

Therefore, for example, Patent Document 1 describes that the amount of cesium transferred to the plant is suppressed by adding zeolite to the soil, and the amount of zeolite added to the soil and the transfer of cesium to the plant are described. The inhibition rate is disclosed. However, the soil usually contains ammonia or potassium as a fertilizer component, and if these elements (ions) exist in zeolite, the effect of capturing cesium may be reduced. Moreover, there is a problem of cost when a large amount of expensive zeolite is used.
Patent Document 2 proposes a decontamination method for soil contaminated with radioactive cesium. As in this proposal, it is important to decontaminate radioactive cesium in soil to reduce its content, but there is a problem that it takes enormous costs and time.

  Therefore, when planting such as vegetables and fruits is cultivated in soil containing radioactive cesium, it is possible to suppress the transfer of radioactive cesium to plants, and it is possible to cultivate plants safely, without cost and time. It is desired to provide a plant migration inhibitor of radioactive cesium that can be produced and a method for growing plants.

JP 2013-224930 A JP 2013-178177 A

  An object of the present invention is to solve the above-described problems and achieve the following objects. That is, the present invention can suppress the transfer of radioactive cesium to the plant when the plant is cultivated in soil containing the radioactive cesium, and can suppress the plant transfer of the radioactive cesium that can be safely cultivated and eaten. An object is to provide an agent and a method for growing a plant.

Means for solving the problems are as follows. That is,
<1> A radioactive cesium plant migration inhibitor comprising a solid content containing iron hydroxide and sulfate.
<2> The plant migration inhibitor of radioactive cesium according to <1>, wherein the iron hydroxide is Fe (OH) ₃ .
<3> The radioactive cesium plant according to any one of <1> to <2>, wherein the sulfate is at least one selected from CaSO ₄ , K ₂ SO ₄ , Na ₂ SO ₄ , and MgSO _4. It is a migration inhibitor.
<4> The radioactive cesium plant migration inhibitor according to any one of <1> to <3>, wherein the solid content further contains CaO.
<5> The radioactive cesium plant migration inhibitor according to any one of <1> to <4>, wherein the solid content further contains SiO ₂ .
<6> The plant migration inhibitor of radioactive cesium according to any one of <1> to <5>, wherein the content of iron hydroxide in the solid content is 25% by mass or more.
<7> After adding a ferric salt to ferrous sulfide ore mineral water containing heavy metals other than ferrous iron and the ferrous iron, an alkali is added to adjust the pH to 3.2 or higher, and the pH of 3.2 or higher is set. A removal step of removing a portion of the ferrous iron and heavy metals other than the ferrous iron by forming a precipitate of ferric hydroxide while holding and removing the hydroxide precipitate by solid-liquid separation;
An oxidation step of oxidizing divalent iron contained in the treatment liquid of the iron sulfide ore water after removing heavy metals other than ferrous iron using an oxidizing agent to trivalent iron;
A first neutralization step of neutralizing the treatment liquid after the oxidation step to pH 4.0 to 4.5 with a first neutralizing agent;
A second neutralization step of neutralizing the treatment liquid after the first neutralization step to a pH of 7.3 to 8.3 with a second neutralizing agent;
A solid-liquid separation step for solid-liquid separation of the treatment liquid after the second neutralization step;
It is a manufacturing method of the plant migration inhibitor of radioactive cesium characterized by including this.
<8> The method for producing a radioactive cesium plant migration inhibitor according to <7>, wherein the first neutralizing agent is calcium carbonate.
<9> The method for producing a radioactive cesium plant migration inhibitor according to any one of <7> to <8>, wherein the second neutralizing agent is slaked lime.
<10> The method for producing a radioactive cesium plant migration inhibitor according to any one of <7> to <9>, wherein the ferric salt is ferric polysulfate.
<11> The plant migration inhibitor of radioactive cesium according to any one of <1> to <6> is sprayed on soil containing 100 Bq / kg or more of radioactive cesium, and the plant is grown in the soil. It is a characteristic plant growth method.
<12> The plant growth method according to <11>, wherein the soil is soil containing 500 Bq / kg or more of radioactive cesium.

  According to the present invention, the conventional problems can be solved, and when a plant is cultivated in soil containing radioactive cesium, the transfer of radioactive cesium to the plant can be suppressed, and the plant can be cultivated safely, It is possible to provide a plant migration inhibitor of radioactive cesium that can be eaten and a plant growth method.

FIG. 1 is a process diagram showing an example of a method for producing a plant migration inhibitor of radioactive cesium used in the present invention.

(Plant migration inhibitor of radioactive cesium)
The plant migration inhibitor of radioactive cesium of the present invention contains a solid content containing iron hydroxide and sulfate, and further contains other components as necessary.

<Solid content containing iron hydroxide and sulfate>
The solid content containing iron hydroxide and sulfate is considered to form a double salt with iron hydroxide and sulfate, and may further contain calcium ions or the like in its structure. Radioactive cesium ions are ion-exchanged with solid salt metal ions in the solid content or adsorbed to the solid content to form a cesium-containing double salt, making it poorly soluble in water and suppressing the absorption of radioactive cesium into plants it is conceivable that.
The iron hydroxide is preferably Fe (OH) ₃ , and the sulfate is preferably at least one selected from CaSO ₄ , K ₂ SO ₄ , Na ₂ SO ₄ , and MgSO ₄ . Moreover, the solid particles are further, CaO, preferably contains SiO _2. The content of iron hydroxide in the solid content is preferably 25% by mass or more.
In addition, as components other than the solid content of the plant migration inhibitor of radioactive cesium, metal components such as moisture and Al, Zn, Mn, and Cu may be included.
The above-mentioned plant migration inhibitor of radioactive cesium containing solids containing iron hydroxide and sulfate can be obtained as a neutralized residue after treating the iron sulfide ore mineral water described below and manufactured at low cost. It is possible to recycle the waste from the iron sulfide ore water.
Hereinafter, the manufacturing method of the plant migration inhibitor of the radioactive cesium containing the solid content containing iron hydroxide and a sulfate will be described.

(Method for producing plant migration inhibitor of radioactive cesium)
The method for producing a radioactive cesium plant migration inhibitor of the present invention includes a removal step, an oxidation step, a first neutralization step, a second neutralization step, and a solid-liquid separation step, and further required. According to other steps. The method for producing the radioactive cesium plant migration inhibitor is performed, for example, by the process flow shown in FIG.

<< Removal process >>
In the removing step, after adding a ferric salt to ferrous sulfide ore water containing heavy metals other than ferrous iron and the ferrous iron, an alkali is added to obtain a pH of 3.2 or more, and the pH of 3.2 or more. In the step of removing a part of the ferrous iron and heavy metals other than the ferrous iron by forming a ferric hydroxide precipitate while maintaining the state and removing the hydroxide precipitate by solid-liquid separation. is there. As a result, part of the ferrous iron is also removed in this step.

-Iron sulfide mineral water containing ferrous iron and heavy metals other than ferrous iron-
The iron sulfide ore mineral water containing the ferrous iron and heavy metals other than the ferrous iron is acidic water, has a large amount, and must be treated semipermanently. Therefore, it is desired to treat it safely and effectively. It is rare.

There is no restriction | limiting in particular as a density | concentration of the bivalent iron ion contained in the iron sulfide ore mineral water containing heavy metals other than said ferrous iron and this ferrous iron, Although it can select suitably according to the objective, 500 ppm ~ 3,000 ppm is preferred.
Examples of the heavy metal component other than the ferrous iron contained in the iron sulfide ore mineral water containing the ferrous iron and heavy metals other than the ferrous iron include, for example, arsenic acid, arsenous acid, selenic acid, selenous acid, chromic acid, etc. Oxyacid anion, copper, zinc, manganese, cadmium and the like.

-Ferric salt-
There is no restriction | limiting in particular as said ferric salt, Although it can select suitably according to the objective, Poly ferric sulfate is preferable.
The polyferric sulfate has the formula: [Fe ₂ (OH) _n (SO ₄ ) _{3 -n / 2} ] _m [wherein n <2 and m> 10. It is a compound represented by this.
There is no restriction | limiting in particular as said polyferric sulfate, What was synthesize | combined suitably may be used and a commercial item may be used. Examples of the commercially available products include Polytetsu R (manufactured by Nippon Steel Mining Co., Ltd.), Bioferric (manufactured by Sonekura Mining Co., Ltd.), and the like.
When the ferric sulfate is added to the iron sulfide ore mineral water containing the ferrous metal and heavy metals other than the ferrous iron, ferric hydroxide (Fe (OH) ₃ ) is precipitated, and the precipitated water Ferric oxide aggregates and settles. When ferric hydroxide precipitates and aggregates, for example, arsenous acid (H ₃ AsO ₃ ) other than the ferrous iron in a liquid containing ferrous iron and heavy metals other than the ferrous iron, etc. It is thought that heavy metals are captured by coprecipitation

The amount of polyferric sulfate added as the ferric salt is not particularly limited and can be appropriately selected according to the purpose. However, the sulfur containing a heavy metal other than the ferrous iron and the ferrous iron. 10 g / L or less is preferable with respect to iron ore deposit water, 0.5 g / L to 10 g / L is more preferable, and 1 g / L to 5 g / L is still more preferable.
If the amount added is less than 0.5 g / L, the effect of removing heavy metals other than ferrous iron may be reduced. If it exceeds 10 g / L, the amount of alkali consumption increases and the cost is high. turn into.

-Alkali-
There is no restriction | limiting in particular as said alkali, According to the objective, it can select suitably, For example, caustic soda (NaOH), caustic potash (KOH); lime, quicklime (CaO), slaked lime (Ca (OH) ₂ ), carbonic acid Examples include calcium (Ca) -based alkali agents such as calcium; magnesium (Mg) -based alkali agents such as magnesium oxide and magnesium hydroxide. These may be used individually by 1 type and may use 2 or more types together.

-PH adjustment-
After adding ferric polysulfate as the ferric salt to the iron sulfide ore mineral water containing heavy metals other than the ferrous iron and the ferrous iron, the pH is adjusted to 3.2 or more by adding an alkali. It is preferable to adjust the pH to 3.6 to 4.5. A ferric hydroxide precipitate is formed while maintaining the pH at 3.2 or higher, and the ferric hydroxide precipitate is removed by solid-liquid separation.
If the pH is less than 3.2, the ability to remove heavy metals other than ferrous iron may decrease. If the pH exceeds 4.5, the amount of ferrous iron gradually increases. When the pH increases to 6 or more, the amount of starch generated increases rapidly, so that the pH is more preferably 3.6 to 4.5. When the pH is in the more preferable range, it is advantageous from the viewpoint of removing heavy metals other than ferrous iron.
The pH can be measured by, for example, a commercially available pH meter.

<< Oxidation process >>
The oxidation step is a step of oxidizing divalent iron contained in the treatment liquid of the iron sulfide ore water after removing heavy metals other than ferrous iron using an oxidizing agent to trivalent iron.
The ferrous iron oxidation method is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include iron-oxidizing bacteria, hypochlorite, hydrogen peroxide, air, oxygen gas, ozone gas, and ozone. Water, etc. Among these, iron-oxidizing bacteria are particularly preferable from the viewpoint of drug cost and oxidation efficiency.

As the iron-oxidizing bacteria, not as long as it has an oxidizing power particularly limited in the treatment solution after said removing step, may be appropriately selected depending on the intended purpose, for example, Thiobacillus Ferro oxidant (Thiobachillus ferrooxidans) Etc. Among these, thiobacillus ferrooxidant is particularly preferable. Thiobacillus ferrooxidant lives at pH 2 to 3 and has oxidative activity. Therefore, divalent iron can be rapidly oxidized to trivalent iron in an environment having a low pH.
The oxidation reaction of divalent iron by the iron-oxidizing bacteria is represented by the following formula.
Fe ²⁺ + H ⁺ +1/4 O ₂ → Fe ³⁺ + 1/2 H ₂ O
The addition of the iron-oxidizing bacteria to the treatment solution after the removing step may be performed at once, or may be performed in several times. When continuous oxidation treatment is performed, it is preferable to appropriately supplement iron-oxidizing bacteria.
The amount of the iron-oxidizing bacteria added to the treatment solution after the removal step can be appropriately selected according to the concentration of divalent iron in the treatment solution after the removal step.

<< First neutralization step >>
The first neutralization step is a step of neutralizing the treatment solution after the oxidation step to pH 4.0 to 4.5 with a first neutralizing agent.
There is no restriction | limiting in particular as said 1st neutralizing agent, Although it can select suitably according to the objective, From the point of chemical | medical agent cost, a calcium carbonate is preferable.
The neutralization reaction in the first neutralization step is, for example, as follows.
Fe ₂ (SO ₄ ) ₃ + 3CaCO ₃ →
2Fe (OH) ₃ ↓ + 3CaSO ₄ ↓ + 3CO ₂ ↑
The addition of the first neutralizing agent to the solution after the oxidation step may be performed at once, or may be performed in several steps.

<< Second neutralization step >>
The second neutralization step is a step of neutralizing the treatment liquid after the first neutralization step to a pH of 7.3 to 8.3 with a second neutralizing agent. The pH is defined by the drainage standard for neutralized treated water.
There is no restriction | limiting in particular as said 2nd neutralizing agent, Although it can select suitably according to the objective, From the point of the sedimentation property of the generated temple, slaked lime is preferable.
The neutralization reaction in the second neutralization step is, for example, as follows.
Fe ₂ (SO ₄ ) ₃ + 3Ca (OH) ₂ → 2Fe (OH) ₃ ↓ + 3CaSO ₄ ↓
The addition of the second neutralizing agent to the liquid after the first neutralization step may be performed at once, or may be performed in several steps.

<< Solid-liquid separation process >>
The solid-liquid separation step is a step of solid-liquid separation of the treatment liquid after the second neutralization step. By this solid-liquid separation step, a plant migration inhibitor of radioactive cesium containing a solid content containing iron hydroxide and sulfate is obtained.
There is no restriction | limiting in particular as said solid-liquid separation, According to the objective, it can select suitably, For example, membrane filtration, suction filtration, pressure filtration, sedimentation separation, centrifugation, etc. are mentioned.
Specifically, the solid-liquid separation step includes radioactive cesium containing a solid content containing iron hydroxide and sulfate having a water content of 60% or less after removing water by a filter press after solid-liquid separation with a thickener. Plant migration inhibitor.

The content of iron hydroxide in the solid content containing the obtained iron hydroxide and sulfate is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 25% by mass or more, and 50% by mass. The above is more preferable. When the content of the iron hydroxide is less than 25% by mass, the effect of suppressing the migration of radioactive cesium to plants may not be obtained. That is, the solid content containing iron hydroxide and sulfate is preferably a mixture or double salt of iron hydroxide and sulfate.
In addition to iron hydroxide (Fe (OH) ₃ or the like), the solid content containing iron hydroxide and sulfate includes, for example, CaSO ₄ , K ₂ SO ₄ , Na ₂ SO ₄ , and MgSO ₄ as sulfates. comprises at least one selected from, CaO, aluminum hydroxide, oxide or hydroxide such as SiO _2, further, Al, Zn, Mn, may contain such trace metal components such as Cu. It should be noted that heavy metals such as Cd, Cr, and As are removed in the removing step, and the level is not detected by a normal analyzer.

  The obtained solid content containing iron hydroxide and sulfate has an excellent effect of suppressing the transfer of radioactive cesium to plants, and can be used as a plant transfer inhibitor of radioactive cesium as it is, as described below. It can be used for the plant growth method of the present invention. The radioactive cesium plant migration inhibitor may contain moisture in addition to the solid content.

(Plant growth method)
The plant growth method of the present invention is a method for spraying the radioactive cesium plant migration inhibitor of the present invention containing solids containing iron hydroxide and sulfate to the soil containing radioactive cesium, and Cultivate. In the present invention, the soil containing radioactive cesium refers to soil containing 100 Bq / kg or more of radioactive cesium, and more preferably applied is soil containing 500 Bq / kg or more of radioactive cesium.

  The target plant used in the plant growth method is not particularly limited and may be appropriately selected depending on the intended purpose. For example, cucurbitaceae, solanaceae, legumes, roses, cruciferous, asteraceae, seri , Azatheaceae, Gramineae, Aoiaceae, Araceae, Lamiaceae, Gingeraceae, Water Lily Family, Araceae Family, Compositae, Rose Family, Araceae Family, Brassica Family, Brassicaceae Family, Gentian Family, Gentianaceae, Bomanohusa Family, Legume Family, Button Family, Iridaceae Family, Eggplant Family, Amaryllidaceae Family, Orchidaceae Family, Azalea Family, Rubiaceae Family, Willow Family, Azalea Family, Azalea Family, Magnoliaceae, Primrose Family, Scarceae Family, Labiatae Family, Auriculariaceae, crassulaceae, buttercupaceae, cinnamonaceae, cactiaceae, ferns, araliaceae, mulberry family, cassavaceae, pineapple family, cranaceae family, Nymphalidae, Pepperaceae, Takadaidai, Yukinoshita, Akabana, Aoi, Futomidae, Camellia, Camellia, Cutlery, Pottery, Rose, Grape, Mulberry, Persimmonaceae, Azalea , Akibiaceae, Matatabidae, Passifloridae, Citrusaceae, Ursiaceae, Pineappleaceae, Fruitberry, Algae and the like.

  More specifically, rice, wheat, cucumber, melon, pumpkin, bitter gourd, zucchini, watermelon, shirori, tougan, loofah, kinsiuri, tomato, pepper, pepper, eggplant, pepino, shiitsu, pea, kidney bean, cowpea, edamame, broad bean , Winged bean, peas, green beans, peas, strawberries, corn, okra, broccoli, silkworm radish, watercress, komatsuna, tsukena, lettuce, buffalo, garlic, edible chrysanthemum, celery, parsley, honeybee, seri, spring onion, leek, asparagus , Spinach, Okajiki, Udo, Perilla, Ginger, Japanese radish, Japanese radish, Japanese radish, Turnip, Horseradish, Radish, Rutabaka, Kokabu, Garlic, Japanese radish, lotus root, taro etc. Astor, Rhodanthese, Thistle, Nadesico, Stock, Hanana, Stachys, Turkey, Snapdragon, Sweetpea, Hanashob, Chrysanthemum, Liatris, Gerbera, Margaret, Miyakowasle, Shasta Daisy, Carnation, Stucons, Gentian, Peonies , Dahlia, color, gladiolus, iris, freesia, tulip, narcissus, amaryllis, cymbidium, dracaena, rose, bokeh, cherry blossom, peach, plum, kodemari, raspberry, rowan, dogwood, sanche, sandanka, burbadia, willow, azalea, Forsythia, magnolia, cilanaria, dimorphoseca, primula, petunia, begonia, gentian, coleus, geranium, pelargonium, roqueya, Nsrum, clematis, lily of the valley, saintpaulia, cyclamen, ranunculus, gloxinia, dendrome, cattleya, phalaenopsis, banda, shrimp drum, oncidium, cactus cactus, crab cactus, peafowl cactus, kalanchoe, nephrolepis, asiattum, taniwata Spatiflam, singonium, orchid orchid, ciefrera, hedera, rubber tree, dracaena, cordierine, bridal veil, bromeliad, karateya, croton, peperomia, poinsettia, hydrandia, fuchsia, hibiscus, gardenia, gorghum, camellia, bougainvillea, etc. Japanese pear, peach, sweet cherry, plum, apple, prune, nectarine, apricot, razz Berries, plums, grapes, figs, oysters, blueberries, akebi, kiwifruit, passion fruit, loquat, shrimp mandarin, marcolet, lemon, yuzu, buddha tangerine, hassaku, buntan, flower yuzu, kumquat, seminole, yeokan, navel orange, Examples include fruit trees such as encore, nova, hyuga summer, lime, sudachi, kabosu, late birch, tankan, mango, pineapple, and guava; or algae.

There is no restriction | limiting in particular as a spraying method to the soil of the plant migration inhibitor of the said radioactive cesium, According to the kind of plant, quantity, etc., it can select suitably.
The amount of the radioactive cesium plant migration inhibitor sprayed onto the soil is not particularly limited and can be selected according to the purpose. For example, as a guideline, 10 mass% or more with respect to a predetermined volume of soil necessary for plant growth. It is preferable to spray a quantity of.
There is no restriction | limiting in particular as the cultivation method of the said plant, Although it can select suitably according to the kind of plant, quantity, etc., it can carry out by the method currently performed normally.

  According to the plant growth method of the present invention using the radioactive cesium plant migration inhibitor of the present invention, it is possible to suppress the migration (absorption) of radioactive cesium to a plant at a low cost and without inhibiting the growth of the plant. Can do. As a result, even if plants are cultivated in soil containing radioactive cesium, it is possible to achieve a radioactive cesium content in plants of 100 Bq / kg or less, which is the standard value for radioactive cesium in general foods (vegetables, fruits, etc.) And can grow plants safely.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

(Production Example 1)
-Production of plant migration inhibitor of radioactive cesium-
Using the mine wastewater of the iron sulfide deposit having the composition shown in Table 1 below, a plant migration inhibitor of radioactive cesium containing a solid content containing iron hydroxide and sulfate was produced by the above-described method shown in FIG.

  First, 0.7 g / L of polyferric sulfate (Bioferric, manufactured by Sonekura Mining Co., Ltd.) as a ferric salt was added to the mine wastewater of the iron sulfide deposit at 28 ° C. The waste water containing ferric sulfate was stirred, and then the pH was adjusted to 3.6 while adding 24 mass% caustic soda. While maintaining the pH of 3.6, a ferric hydroxide precipitate was formed and separated into a slurry slurry and a supernatant by a thickener (removal step). In addition, pH was measured using the pH meter (HORIBA, Ltd. make, HORIBA 9625-10D).

Next, using the iron Thiobacillus-ferrooxidans as oxidizing bacteria (Thiobachillus ferrooxidans), it was oxidized divalent iron contained in the filtrate after the removing step trivalent iron (oxidation step).
Next, the treatment liquid after the oxidation step was separated into bacterial oxide slurry and supernatant water by a thickener.
Next, the supernatant water after the oxidation step was neutralized with calcium carbonate so as to be in the range of pH 4.0 to 4.5 (first neutralization step).
Next, the liquid after the first neutralization step was neutralized with slaked lime so as to be in the range of pH 7.3 to 8.3 (second neutralization step).
Next, after the liquid after the second neutralization step is solid-liquid separated with a thickener, the plant migration inhibitor of radioactive cesium containing a solid content containing iron hydroxide and sulfate having a water content of 60% or less by a filter press Got.
The composition of the solid content of the obtained plant migration inhibitor of radioactive cesium is shown in Table 2 below.

From the results of Table 2, the obtained plant migration inhibitor of radioactive cesium was 52% by mass of iron hydroxide (Fe (OH) ₃ ), 18.3% by mass of CaSO ₄ and 5.3% by mass of CaO ( CaSO ₄ and CaO in total 23.6% by mass), SiO ₂ 3% by mass, moisture 21% by mass, and heavy metals such as Cd, Cr and As were found to be below the detection limit of analysis. . In addition, the unit of content of Cd, Cr, As is mass ppm.
Here, the content of Fe (OH) _{3 in} the radioactive cesium plant migration inhibitor is analyzed and measured based on JIS K0102-57.4, and the content of Fe in the radioactive cesium plant migration inhibitor is all. of Fe was calculated content of Fe _{(OH) 3} as an Fe _{(OH) 3.} Wherein for CaSO ₄ and CaO in radioactive cesium plant migration inhibitor, the radioactive cesium content of Ca in the plant during migration inhibitor analyzes and measured according to JIS K0102-50.3, the radioactive cesium plant migration inhibitor The content of SO ₄ is analyzed and measured by ICP, the content of CaSO ₄ is calculated assuming that all SO ₄ is CaSO ₄ , and all Ca except Ca consumed by CaSO ₄ is CaO. The content of CaO was calculated as there was.
The content of SiO ₂ in the radioactive cesium plant migration inhibitor, wherein the content of Si in the radioactive cesium plant migration inhibitor analyzes and measurements in ICP, all of Si-containing SiO ₂ as a SiO ₂ The amount was calculated.
Cd in the radioactive cesium plant migration inhibitor was analyzed and measured based on JIS K0102-55.3.
Cr in the radioactive cesium plant migration inhibitor was analyzed and measured based on JIS K0102-55.1.
As in the radioactive cesium plant migration inhibitor was analyzed and measured based on JIS K0102-61.3.
The compound form of _{Fe (OH) 3, CaSO 4} , CaO or the like in the radioactive cesium plant migration inhibitors identified by X-ray diffraction analysis of solids, was confirmed.

<Original soil>
The soil in Fukushima city that was radioactively contaminated by the accident at TEPCO's Fukushima Daiichi nuclear power plant was collected and its radiocesium content was measured as follows. The results are shown in Table 3.

<< Measurement of Radiocesium Content >>
It measured with the gamma ray spectrometer (EMF Japan Co., Ltd. make, EMF211 type | mold) using the NaI scintillation detector.

<"Radiocesium plant migration inhibitor" as an additive>
The “radiocesium plant migration inhibitor” prepared in Production Example 1 was used as an additive. When the radioactive cesium content of the “plant migration inhibitor of radioactive cesium” was measured in the same manner as described above, it was not detected.

<"Kun Charcoal" as an additive>
“Kun Charcoal” is charcoal made from rice husk and has many pores, and has been conventionally used as a soil conditioner for water retention, air permeability and pH correction of acidic soil. When the radioactive cesium content of this “kun charcoal” was measured in the same manner as described above, it was not detected.

<"Adjusted soil" as an additive>
Soil not contaminated with radioactive cesium in Okayama Prefecture was used as an additive. When the radioactive cesium content of this “adjusted soil” was measured in the same manner as described above, it was not detected.

Example 1
<Cultivation of silkworm radish>
For 8 kg of the original soil, the mixed soil (mixing ratio 20% by mass) added with 2 kg of the “plant migration inhibitor of radioactive cesium” of Production Example 1 as an additive is put in a planter (250 mm × 90 mm × 50 mm), Seed seeds of silkworm radish.
A planter with seeds of silkworm radish was installed in the greenhouse and cultivated normally. About 500 g of golden radish could be harvested by cultivating for 18 days after sowing.
About the obtained silkworm radish, the radioactive cesium (Cs) content was measured in the same manner as described above. Moreover, potassium (K) content in mixed soil was measured as follows. The results are shown in Table 3.

<< Measurement of potassium content in soil >>
The potassium content of the soil was measured with an atomic absorption photometer (manufactured by Hitachi, Ltd., Z-8100). In addition, the reason why potassium (K) in soil was measured is that there is a report example in which the concentration affects the transfer of radioactive cesium to plants, and a reference value is obtained. It is known that when the potassium ion concentration in soil is high, the rate of transfer of radioactive cesium to plants decreases. The recommended potassium content of 25 mg / 100 g is recommended. Moreover, soluble potassium and those which are not exist exist, and it has been reported that the cesium absorption inhibitory effect of soluble potassium is large.
On the other hand, potassium contains a radioisotope, potassium-40, at a constant ratio, emits gamma rays like cesium, and has a high migration coefficient, so that it is easily absorbed by plants. Excessive potassium fertilization of soil has been shown to be a concern that encourages internal exposure via crops (Reference: Koichi Yuda, “Considering radioactive contamination of crops and farmland, forest ecosystem) "reference).

(Comparative Example 1)
<Cultivation of silkworm radish>
The mixed soil (mixing ratio 20% by volume) to which 2 L of the above “kunchar” was added as an additive to the original soil 8 L was put in a planter (250 mm × 90 mm × 50 mm), and seedling of silkworm radish was performed.
A planter on which seeds of silkworm radish were sown (faced) was installed in a greenhouse, and normal cultivation was performed. About 500 g of golden radish could be harvested by cultivating for 18 days after sowing.
About the obtained silkworm radish, the radioactive cesium (Cs) content and the potassium (K) content of the soil were measured in the same manner as described above. The results are shown in Table 3.

(Comparative Example 2)
<Cultivation of silkworm radish>
Mixed soil (mixing ratio 20% by mass) to which 2 kg of the above-mentioned “adjusted soil” was added as an additive to 8 kg of the original soil was placed in a planter (250 mm × 90 mm × 50 mm), and seedling of silkworm radish was performed.
A planter on which seeds of silkworm radish were sown (faced) was installed in a greenhouse, and normal cultivation was performed. About 500 g of golden radish could be harvested by cultivating for 18 days after sowing.
About the obtained silkworm radish, the radioactive cesium (Cs) content and the potassium (K) content of the soil were measured in the same manner as described above. The results are shown in Table 3.

In Table 3, “cesium content (%) (compared with adjusted soil)” and “cesium migration coefficient” were calculated as follows.
* "Cesium content (%) (compared with adjusted soil)": Reduction rate when Comparative Example 2 is 100%. When expressed by the formula, the reduction rate = (Cs content of Comparative Example 2−Cs content of Example 1 and Comparative Example 1) ÷ (Cs content of Comparative Example 2) × 100.
* “Cesium transfer coefficient”: the ratio between the amount of Cs contained in the soil unit weight and the amount of Cs contained in the unit weight of the crop cultivated in the soil. Expressed by the formula, Cs134 migration coefficient of Example 1 = Cs134 content of Example 1 ÷ Cs134 content of the original soil.

  From the result of Table 3, Example 1 which added the "plant migration inhibitor of radioactive cesium" is high compared with the comparative example 1 which added "kun charcoal", and the comparative example 2 which added "adjustment soil". It was observed that radioactive cesium has an inhibitory effect on plant migration.

(Comparative Example 3)
<Cultivation of Japanese radish>
The mixed soil (mixing ratio 20% by mass) added with 2 kg of the above-mentioned “adjusted soil” as an additive to the original soil 8 kg is put into a planter (570 mm × 110 mm × 100 mm), and radish seed pods (sown) Went.
A planter with seeds of radish on the 20th was installed in the greenhouse and was cultivated normally. By cultivating for 78 days after sowing, about 200 g of radish was harvested.
About the obtained 20 day radish, radioactive cesium (Cs) content was measured like the above. The results are shown in Table 4.

(Example 2)
<Cultivation of Japanese radish>
With respect to 8 kg of the original soil, the mixed soil (mixing ratio 20% by mass) added with 2 kg of the “plant migration inhibitor of radioactive cesium” of the production example 1 as an additive is put in a planter (570 mm × 110 mm × 100 mm), Twenty days of radish seed pods (sown).
A planter with seeds of radish on the 20th was installed in the greenhouse and was cultivated normally. By cultivating for 78 days after sowing, about 200 g of radish was harvested.
About the obtained 20 day radish, radioactive cesium (Cs) content was measured like the above. The results are shown in Table 4.

In Table 4, “cesium content (%) (compared with adjusted soil)” and “cesium migration coefficient” were calculated as follows.
* "Cesium content (%) (compared with adjusted soil)": Reduction rate when Comparative Example 3 is 100%.
* “Cesium transfer coefficient”: the ratio between the amount of cesium (Cs) contained in the soil unit weight and the amount of cesium (Cs) contained in the unit weight of the crop cultivated in the soil.

  From the result of Table 4, Example 2 which added "the plant migration inhibitor of radioactive cesium" has a high migration inhibitory effect to the plant of radioactive cesium compared with the comparative example 3 which added "control soil". Was recognized.

  The plant migration inhibitor of radioactive cesium of the present invention can suppress the migration of radioactive cesium to plants when cultivated in soil containing plant radioactive cesium, so various plants such as vegetables and fruits It can be widely applied to safe cultivation.

Claims (4)

After adding ferric salt to ferrous sulfide ore water containing heavy metals other than ferrous iron and ferrous iron, alkali is added to adjust the pH to 3.2 or higher, while maintaining the pH of 3.2 or higher. A removal step of forming a precipitate of ferric hydroxide and removing a portion of the ferrous metal and heavy metals other than the ferrous iron by removing the hydroxide precipitate by solid-liquid separation;
An oxidation step of oxidizing divalent iron contained in the treatment liquid of the iron sulfide ore water after removing heavy metals other than ferrous iron using an oxidizing agent to trivalent iron;
A first neutralization step of neutralizing the treatment liquid after the oxidation step to pH 4.0 to 4.5 with a first neutralizing agent;
A second neutralization step of neutralizing the treatment liquid after the first neutralization step to a pH of 7.3 to 8.3 with a second neutralizing agent;
A solid-liquid separation step for solid-liquid separation of the treatment liquid after the second neutralization step;
A method for producing a plant migration inhibitor of radioactive cesium, comprising:   The method for producing a plant migration inhibitor of radioactive cesium according to claim 1, wherein the first neutralizing agent is calcium carbonate.   The method for producing a radioactive cesium plant migration inhibitor according to claim 1, wherein the second neutralizing agent is slaked lime.   The method for producing a plant migration inhibitor of radioactive cesium according to any one of claims 1 to 3, wherein the ferric salt is polyferric sulfate.