JP2014176777A - Radioactive cesium adsorbing material, and method for cleaning radioactively contaminated water by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radioactive cesium adsorbing material by which the water contaminated by radioactive cesium can efficiently be cleaned and which has high productivity and to provide a method for cleaning radioactively contaminated water by using the radioactive cesium adsorbing material.SOLUTION: The radioactive cesium adsorbing material and the method for cleaning radioactively contaminated water by using the radioactive cesium adsorbing material are disclosed. The radioactive cesium adsorbing material is obtained by imparting Prussian blue to a pulp-fibrous base material. The contaminated water containing radioactive cesium can efficiently be cleaned by the radioactive cesium adsorbing material. For example, even when the contaminated water, which is contained in the soil contaminated with the radioactive cesium, is cleaned, the radioactive cesium adsorbing material can efficiently clean the contaminated water while being hardly clogged. Discarded resources such as used paper can be utilized in the radioactive cesium adsorbing material and consequently the production efficiency thereof can be made higher and the mass production thereof can be applied.

Description

  The present invention relates to a radioactive cesium adsorbent and a method for purifying radioactive polluted water using the same, and more specifically, a radioactive cesium adsorbent capable of efficiently purifying water contaminated with radioactive substances such as radioactive cesium. The present invention also relates to a method for purifying radioactive polluted water using the same.

  The Great East Japan Earthquake that occurred in 2011 caused tremendous damage to Japan due to the Tohoku-Pacific Ocean Earthquake and the accompanying tsunami.

  Among them, the diffusion of a large amount of radioactive material that occurred in Fukushima Prefecture is still serious as it has forced long-term evacuation of local residents. This diffusion of radioactive materials causes soil contamination by radioactive materials in many places in the Tohoku region, and removal of radioactive materials has become an urgent issue.

  In particular, soil contaminated with radioactive materials also contaminates local rivers and groundwater sources with rainwater. The presence of water contaminated with radioactive substances (contaminated water) can be said to be a major factor that hinders the reconstruction of the Tohoku region as well as the problem of soil contamination.

  In the purification of the contaminated water, various kinds of radioactive cesium adsorbents have been researched and developed so far as Prussian blue, which is a kind of blue pigment, is effective in removing radioactive cesium. For example, a product in which Prussian blue is supported on a nonwoven fabric such as polyester, polyethylene terephthalate, polypropylene, and polyamide is commercially available.

  However, in such a conventional radioactive cesium adsorbent, improvement in purification efficiency is desired in that it is likely to be clogged in purification of contaminated water containing soil together. Further, improvement in productivity is desired in the production of such an adsorbent.

  The advent of an effective radioactive cesium adsorbent with high versatility and enhanced production efficiency is strongly expected.

  An object of the present invention is to solve the above-mentioned problems, and the object of the present invention is to provide radioactive cesium that can efficiently purify contaminated water contaminated with radioactive cesium and has improved productivity. An object is to provide an adsorbent and a method for purifying radioactive polluted water using the adsorbent.

  The present invention is a radioactive cesium adsorbent obtained by adding Prussian blue to a pulp fiber base material.

  In one embodiment, the substrate is waste paper, cation exchange paper or a mixed paper thereof.

  In one embodiment, the Prussian blue is contained in a proportion of 1% by mass to 50% by mass with respect to the total mass.

  In one embodiment, the radioactive cesium is at least one radioactive substance selected from the group consisting of cesium 137 and cesium 134.

  The present invention is also a method for producing a radioactive cesium adsorbent, comprising the step of imparting Prussian blue to a pulp fibrous substrate.

  In one embodiment, the application of the Prussian blue to the substrate is performed by immersing the substrate in an aqueous solution containing the Prussian blue.

  In one embodiment, the substrate is waste paper, cation exchange paper or a mixed paper thereof.

  In one embodiment, the Prussian blue is contained in a proportion of 0.1% by mass to 50% by mass with respect to the total mass.

  In one embodiment, the radioactive cesium is at least one radioactive substance selected from the group consisting of cesium 137 and cesium 134.

  The present invention is also a method for purifying contaminated water contaminated with radioactive cesium, comprising the step of bringing the radioactive cesium adsorbent into contact with the contaminated water.

  According to the present invention, contaminated water containing radioactive cesium can be efficiently purified. For example, the adsorbent of the present invention is less likely to be clogged during purification of contaminated water contained in soil contaminated with radioactive cesium, and can efficiently purify contaminated water. The present invention can also utilize waste resources such as waste paper, thereby further improving the production efficiency, and is also suitable for mass production.

It is the graph for comparing the performance with respect to the radioactive cesium adsorption material obtained in Example 1 and 2, the conventional Prussian blue carrying nonwoven fabric, or the radioactive cesium contaminated water evaluated by control, Comprising: 10-hour accumulation of radioactive cesium 137 It is a graph which shows the result of having measured the radioactivity. It is a graph for comparing the performance with respect to the radioactive cesium adsorption material obtained in Example 1 and 2, the conventional Prussian blue carrying nonwoven fabric, or the radioactive cesium contamination water evaluated by control, Comprising: 10-hour accumulation of radioactive cesium 134 It is a graph which shows the result of having measured the radioactivity.

  Hereinafter, the present invention will be described in detail.

  The radioactive cesium adsorbent of the present invention is obtained by adding Prussian blue to a pulp fiber base material.

  The pulp fibrous base material constituting the adsorbent of the present invention is, for example, a material containing pulp fibers at a ratio of at least 80% by mass, preferably 95% by mass or more, and more preferably 98% by mass or more. It has a sheet-like form. When the pulp fibrous base material has a sheet-like form, the thickness of the radioactive cesium base material of the present invention is not particularly limited, and is, for example, 0.01 mm to 10 mm, preferably 0.1 mm to 1 mm.

  The pulp fiber base material is preferably a mixed paper made of waste paper, cation exchange paper or a combination thereof. The cation exchange paper can be obtained, for example, by making paper by mixing cellulose fibers such as carboxymethyl cellulose with pulp fibers as appropriate. The pulp fiber content in the cation exchange paper is not particularly limited, but is, for example, 0.1% to 50% based on the mass of the cation exchange paper. Methods and means for papermaking are not particularly limited, and methods and means well known in the art can be used.

  Prussian blue (PB) constituting the adsorbent of the present invention belongs to ferric ferrocyanide, for example, the following formula (I):

In general, it is known as a blue pigment. Prussian blue is a colloidal substance that is not absorbed by the digestive tract, has low toxicity, can be used orally, and is known to bind to certain monovalent cations such as cesium and thallium. It has been.

  In the present invention, Prussian blue is applied to the pulp fibrous base material at a predetermined ratio. Although the content rate of Prussian blue is not particularly limited, it is preferably 0.1% by mass to 50% by mass and more preferably 1% by mass to 30% by mass with respect to the total mass of the adsorbent of the present invention. If the Prussian blue content is less than 0.1% by mass, it may be difficult to efficiently purify contaminated water containing radioactive cesium with respect to the contaminated water. If the Prussian blue content exceeds 50% by mass, the ratio of Prussian blue re-detaching from the adsorbent may increase.

  In the present invention, various methods can be used to apply the Prussian blue to the pulp fibrous base material. For example, (1) the pulp to an aqueous solution containing Prussian blue (hereinafter also referred to as Prussian blue aqueous solution). Immersion of fibrous base material, (2) Spraying Prussian blue aqueous solution onto pulp fibrous base material, (3) Application of Prussian blue aqueous solution onto pulp fibrous base material, (4) Known to pulp fibrous base material Adhesion of Prussian blue using an adhesive component (adhesive or the like) of (5), or (5) a combination of two or more of (1) to (4) may be used.

  Here, as an example of application of the Prussian blue to the pulp fibrous base material, (1) immersion of the pulp fibrous base material in the Prussian blue aqueous solution will be described.

  The Prussian blue aqueous solution is prepared by dissolving or dispersing a predetermined amount of Prussian blue in water (including, for example, tap water, ion-exchanged water, ultrapure water, and electrolytic water). The concentration of the Prussian blue aqueous solution selected for the preparation is, for example, 1 g / L to 300 g / L, preferably 10 g / L to 100 g / L.

  Prussian blue aqueous solution is a component and concentration as long as the above-mentioned Prussian blue does not interfere with the adsorption performance of radioactive cesium. In addition to Prussian blue, adsorption performance for other components (eg, radioactive substances (eg, radioactive cesium, radioactive iodine) And other additives such as a pH adjusting agent). The content of other components can be appropriately selected by those skilled in the art.

  In the immersion of the pulp fibrous base material in the Prussian blue aqueous solution, the bath ratio between the pulp fibrous base material and the Prussian blue aqueous solution is not particularly limited, and an appropriate bath ratio can be set by those skilled in the art. The bath temperature at the time of immersion is not particularly limited. For example, immersion may be performed at room temperature. The immersion time is not necessarily limited because it varies depending on the thickness of the pulp fibrous base material, the concentration of the Prussian blue aqueous solution, and the bath temperature. As the immersion time, for example, an appropriate time can be set by a person skilled in the art. In addition, since the pulp fiber base material is immersed in such an aqueous Prussian blue solution by simply adding the Prussian blue aqueous solution to an aqueous solution of beating used paper, the recycled paper recycling line is used as it is. Productivity can be dramatically improved.

  After the predetermined immersion, the pulp fibrous substrate to which Prussian blue is applied is taken out of the immersion bath and dried.

  Thus, the radioactive cesium adsorption material by which Prussian blue was provided to the pulp fiber base material of this invention can be obtained.

  The radioactive cesium adsorbent of the present invention may be cut into a predetermined size as necessary.

  Next, a method for purifying contaminated water containing radioactive cesium using the radioactive cesium adsorbent of the present invention will be described.

  In purification of contaminated water, the radioactive cesium adsorbent of the present invention is brought into contact with the contaminated water.

  For example, (1) charging the radioactive cesium adsorbent of the present invention into a container containing contaminated water for a predetermined time, (2) cutting the radioactive cesium adsorbent of the present invention as it is or as needed, Packing in a column as a column filler and passing contaminated water therein, (3) Filtering contaminated water using the radioactive cesium adsorbent of the present invention as a kind of filter paper, (4) Above (1) to (3) can be performed multiple times and / or combined. As conditions for the operation accompanying such contact, those skilled in the art can set arbitrary conditions as necessary.

  Thus, radioactive cesium can be efficiently and easily removed from contaminated water containing radioactive cesium. In the radioactive cesium adsorbent of the present invention, the type of radioactive cesium that can be adsorbed is not particularly limited. That is, good adsorption performance can be exhibited for any of radioactive cesium 137, radioactive cesium 134, and combinations thereof.

  After the contaminated water is purified, the radioactive cesium adsorbent of the present invention may be subjected to additional work such as drying as necessary. For example, in accordance with the disposal rules established by each region, local government or country. Discarded.

  EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited by these Examples.

(Example 1: Production of PB replacement paper)
Pulp fibers (manufactured by Wako Pure Chemical Industries, Ltd.) were mixed with carboxymethyl cellulose (“Sunrose (registered trademark) P” manufactured by Nippon Paper Chemicals Co., Ltd.) at a ratio of 10% by mass. The mixture was then beaten so that the fiber surface was fully bonded. Thereafter, this mixture was dispersed in water to prepare a diluted pulp fiber dispersion.

  Paper was made from this pulp fiber dispersion using a nylon net (100 mesh). Next, the obtained paper (base material) was sandwiched between non-woven fabrics and sufficiently pressed using a roller to remove excess moisture. Furthermore, in order to remove the free water remaining in the replacement paper, the replacement paper was obtained by heating with a hot plate at 60 ° C. In addition, this exchange paper has a carboxymethyl group as a cation exchange group by containing carboxymethylcellulose.

  Next, this exchange paper was immersed in a bath containing an aqueous Prussian blue solution prepared in advance to 0.476% by mass at a bath ratio of 1: 100 at room temperature for 30 minutes. After immersion, the replacement paper was taken out of the bath, sufficiently drained, and then air-dried to obtain Prussian blue replacement paper (PB replacement paper) as a radioactive cesium adsorbent.

(Example 2: Production of PB paper)
Prussian blue paper (PB paper), which is a radioactive cesium adsorbent, was obtained in the same manner as in Example 1 except that old newspaper was used instead of the replacement paper containing carboxymethylcellulose and pulp fibers of Example 1. .

(Example 3: Evaluation of adsorption performance of radioactive cesium 137)
After 1 kg of soil collected in Minamisoma City, Fukushima Prefecture in May 2011 was passed through a sieve, it was thoroughly mixed and weighed 20 g at a time to prepare 12 samples. The samples were classified into 4 groups consisting of 3 samples per group.

  Next, 80 g of deionized water was added to each of the samples and mixed thoroughly. Further, the mixture was mixed by inversion over 12 hours, and then returned to the original state and left for 30 minutes. The supernatant portion was removed from each sample and centrifuged at 3000 rpm for 20 minutes. Then, excess soil and waste were removed using filter paper (No. 1 manufactured by Advantech Toyo Co., Ltd.).

  Here, about the obtained filtrate, about 3 groups among 4 groups, PB exchange paper obtained in Example 1 above, PB paper obtained in Example 2 or commercially available as test materials in each group 1 g of Prussian blue non-woven fabric (PB non-woven fabric) (manufactured by Dainichi Seika Kogyo Co., Ltd.) was added. For the remaining one group, no test material was added as a control water group. Thereafter, the test material was immersed in the filtrate of each sample for 30 minutes.

  Then, the test material was taken out from the sample while being sufficiently squeezed out, and filtered using a new filter paper (No. 1 manufactured by Advantech Toyo Co., Ltd.) to remove free Prussian blue, and only filtered water was collected. After weighing 50 g of the obtained filtered water, the accumulated radioactivity of radioactive cesium 137 in each sample for 10 hours was measured using a germanium semiconductor detector (manufactured by SEIKO EG & G). Furthermore, about the accumulated radioactivity of the obtained sample, each group (control water group (Comparative Example 2), PB paper group (Example 1), PB exchange paper group (Example 1), PB nonwoven fabric group (Comparative Example 1) )) The average value of the measurement results was calculated.

  The obtained results are shown in FIG.

  As shown in FIG. 1, it can be seen that the PB exchange paper and PB paper obtained in Examples 1 and 2 adsorbed radioactive cesium 137 efficiently. Further, it can be seen that such adsorption performance has a result equal to or higher than that of a commercially available PB nonwoven fabric (Comparative Example 1). In particular, PB paper (Example 2) removed as much as 33% of the radioactive cesium 137 per gram. On the other hand, it turns out that the PB exchange paper obtained in Example 1 has the adsorption performance of the radioactive cesium 137 which exceeds the commercial PB nonwoven fabric, and is a more efficient radioactive cesium adsorbent.

  Furthermore, about the filtered water obtained above (50 g of each), the germanium semiconductor detector (made by SEIKO EG & G) was also used, The 10-hour accumulation radioactivity of radioactive cesium 134 in each sample was also measured. Moreover, about the accumulated radioactivity of the obtained sample, each group (control water group (Comparative Example 2), PB paper group (Example 1), PB exchange paper group (Example 1), PB nonwoven fabric group (Comparative Example 1) )) The average value of the measurement results was calculated.

  The obtained results are shown in FIG.

  As shown in FIG. 2, the adsorption ability of radioactive cesium 134 was similar to that of radioactive cesium 137, and the PB exchange paper and PB paper obtained in Examples 1 and 2 had excellent adsorption performance. Recognize. Further, such adsorption performance was equivalent or better than that of a commercially available PB nonwoven fabric (Comparative Example 1). In particular, PB paper (Example 2) removed as much as about 46% of the radioactive cesium 137 per gram. On the other hand, it turns out that the PB exchange paper obtained in Example 1 has the adsorption performance of the radioactive cesium 134 which exceeds the commercially available PB nonwoven fabric, and is a more efficient radioactive cesium adsorption material.

  The radioactive cesium adsorbent of the present invention can efficiently purify contaminated water containing radioactive cesium. For this reason, for example, it is useful in the purification work of a disaster site and a disaster area contaminated with radioactive materials by radioactive cesium.

Claims (10)

  A radioactive cesium adsorbent comprising Prussian blue added to a pulp fiber substrate.   The radioactive cesium adsorbent according to claim 1, wherein the substrate is waste paper, cation exchange paper, or a mixed paper thereof.   The radioactive cesium adsorbent according to claim 1 or 2, wherein the Prussian blue is contained in a proportion of 0.1% by mass to 50% by mass with respect to the total mass.   The radioactive cesium adsorbent according to any one of claims 1 to 3, wherein the radioactive cesium is at least one radioactive substance selected from the group consisting of cesium 137 and cesium 134. A method for producing a radioactive cesium adsorbent,
Applying Prussian blue to the pulp fiber substrate.   The method according to claim 5, wherein the application of the Prussian blue to the substrate is performed by immersing the substrate in an aqueous solution containing the Prussian blue.   The method according to claim 5 or 6, wherein the substrate is waste paper, cation exchange paper or a mixed paper thereof.   The method according to any one of claims 5 to 7, wherein the Prussian blue is contained in a proportion of 0.1% by mass to 50% by mass with respect to the total mass.   The method according to claim 5, wherein the radioactive cesium is at least one radioactive substance selected from the group consisting of cesium 137 and cesium 134.   A method for purifying contaminated water contaminated with radioactive cesium, comprising the step of contacting the radioactive cesium adsorbent according to claim 1 with the contaminated water.

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