JP2015206775A - Radioactive substance remover and removal method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a remover for removing a radioactive substance from water contaminated with the radioactive substance.SOLUTION: A remover includes, as a main component, one kind or more kinds of fine powder having grain size of nano-size selected from oxide of iron or iron alloy, or nitride.

Description

  The present invention relates to a removal agent and a removal method for removing radioactive material from water contaminated by the radioactive material.

  Currently, zeolite is known as a removal agent for removing radioactive material from water contaminated by radioactive material, and zeolite is used for wastewater treatment from the Fukushima nuclear power plant. However, the ability to remove cesium, which is a radioactive substance by zeolite, is not sufficient, and unless a large amount of zeolite is used, there is a problem that cesium cannot be removed from contaminated water to a value that can be discharged. Further, there is a problem that zeolite is expensive.

  The present applicant has previously filed a patent application for a radioactive decontamination solution (Patent Document 1). However, the present invention is a decontamination solution for efficiently removing radioactive substances from contaminated soil or the like, but does not remove radioactive materials contained in waste water after decontamination.

  Moreover, the processing method of the radioactive substance contamination soil which insolubilizes the radioactive substance contained in soil by simple operation, without generating an extra waste is proposed (patent document 2). These Patent Documents 1 and 2 are techniques for removing radioactive materials from contaminated soil, and are not for removing radioactive substances from liquid contaminated water.

JP2013-057649A JP2013-108913A

  An object of the present invention is to provide a removing agent for removing the radioactive substance from water contaminated by the radioactive substance, and to provide a removing method using the removing agent.

  The gist of the present invention is a removing agent for removing the radioactive substance from water contaminated by the radioactive substance, and one or more selected from iron or iron alloy oxides or nitrides The main component is a fine powder having a nano-size particle size.

  The fine powder of the present invention has a particle size of less than 1 μm, more preferably 10 to 100 nm. The fine powder of the present invention is dust generated by laser welding or laser cutting of iron or an iron alloy in air or nitrogen, and is obtained as an oxide or a nitride.

  The radioactive substance that can be effectively removed by the radioactive substance removing agent of the present invention is cesium.

  The radioactive substance removing method of the present invention includes a step of preparing a container, and 1 to 30 parts by weight of the radioactive substance removing agent according to any one of the above with respect to 100 parts by weight of water contaminated by the radioactive substance in the container. A step of stirring, a step of stirring the mixture of water and the radioactive substance removing agent in the container, a step of separating the stirred mixture into an iron component and a water component, and discharging the water component from the container Including a step.

  The present invention is a process in which the present inventors are intensively studying a decontamination agent and a decontamination method for radioactively contaminated soil. As a result of discovering that cesium is adsorbed on the ground. Cesium can be adsorbed to such nanoparticles by putting nanoparticle-sized iron or iron alloy oxide or nitride into radioactively contaminated water and stirring. Thereafter, nanoparticles made of iron or an iron alloy adsorbing cesium are magnetized by a magnet. By removing the nanoparticles adsorbing cesium from the contaminated water, water from which cesium has been significantly removed can be obtained.

  The removal agent for removing the radioactive substance from the water contaminated by the radioactive substance of the present invention is a fine powder having one or more kinds of particles selected from iron or an oxide or nitride of an iron alloy and having a nano size. The main component is the body. More specifically, fine powder is smoke or dust generated when a plate or wire made of iron or an iron alloy is laser-irradiated in air or nitrogen, and is welded or cut, and is suspended in the air. It is obtained as a product. This suspended matter is collected by a dust collector or the like. In the welding or cutting process by laser irradiation, iron or an iron alloy is heated and melted to several hundreds of degrees Celsius by light energy, thereby joining or cutting. At that time, a part of iron or iron alloy is scattered as oxide or nitride and floats in the air. The suspended matter is collected by a dust collector or the like and used as the removing agent of the present invention. This suspended matter is recovered as industrial waste, and is not obtained only from, for example, iron oxide. In general, oxides or nitrides of iron or an iron alloy are mainly mixed, and rarely oxides or nitrides of other metals may be mixed. Since these cannot be sized, the collected suspended matter (dust) is used as it is. In a normal embodiment, the main component is an oxide or nitride of iron or an iron alloy, and further includes an oxide or nitride of another metal.

  The particle size of the fine iron powder is so small that it floats in the air, and is composed of less than 1 μm. In particular, the particle size of the fine iron powder used in the present invention is preferably 5 to 500 nm, and more preferably 10 to 100 nm. The smaller the particle size, the larger the surface area of the particles per weight, and the more cesium will be adsorbed. When an experiment was conducted on an iron powder having a particle diameter of 1 μm or more, adsorption of cesium was not observed. The iron alloy is not particularly limited, and may be an alloy of iron and another metal such as molybdenum, chromium, nickel, carbon, aluminum or the like. For metals other than iron or iron alloys, fine powders with the above particle diameters cannot be obtained. Therefore, although no experiment has been performed, there is a possibility of adsorbing cesium. However, in order to separate from water, a metal that is magnetically attached to the magnet is preferable.

  The radioactive substance that can be effectively removed by the radioactive substance removing agent of the present invention is cesium. In particular, the adsorption effect has been confirmed for cesium-137 and cesium-134. Water contaminated with radioactive materials includes high-concentration cooling water discharged from nuclear power plants and the like, and water generated by cleaning soil and houses contaminated with radioactivity.

  The radioactive substance removing method of the present invention includes a step of preparing a container, and a step of adding 1 to 30 parts by weight of the radioactive substance removing agent to 100 parts by weight of water contaminated by the radioactive substance in the container; A step of stirring a mixture of water and radioactive substance removing agent contained in a container, a step of separating the stirred mixture into an iron component and a water component, and a step of discharging the water component from the container. .

  The more radioactive substance removing agent that is charged and stirred with respect to the contaminated water, the more cesium can be adsorbed and removed. However, it is only necessary to remove cesium to a safe range that can be discharged into the natural world, and it is not necessary to make cesium zero. Therefore, it is preferable to increase or decrease the amount corresponding to the amount of cesium contained in the contaminated water. However, about the contaminated water which is a problem now in Fukushima Prefecture, 1-30 weight part of the radioactive substance removal agent of this invention is preferable with respect to 100 weight part of contaminated water.

  A sufficient amount of the removing agent for removing radioactive substances may be added to the contaminated water at a time, or it may be divided into a plurality of times. The removal agent used for the low-concentration contaminated water can be used for the high-concentration contaminated water to efficiently remove radioactive substances.

  The stirring (contact) time between the contaminated water and the radioactive substance removing agent is not particularly limited as long as it can be sufficiently stirred. According to the experiment, the amount of radioactive material removed was almost the same and within the error range both when stirring at 3000 rpm for 15 minutes and when stirring for 3 hours. Therefore, it is considered that it is sufficient to ensure the stirring speed and time that the radioactive substance and the iron fine powder can come into contact with each other by stirring.

  The contaminated water and the radioactive substance removing agent, that is, iron fine powder are sufficiently agitated to adsorb the radioactive substance in the contaminated water to the iron fine powder, and then the water component and the iron component are separated. There are four possible separation methods. The first is a method of precipitating the iron component and draining the supernatant water component by standing. This method has a drawback of requiring time because it precipitates nano-sized fine iron powder. The second is a method of separating the iron component and the water component by centrifugation. The third is a method of filtering with a filter medium finer than the particle size of nano-sized iron fine powder. The fourth is a method of magnetically attaching an iron component to a magnet, particularly an electromagnet. A magnet or the like is disposed outside the container. These can be used in appropriate combination.

  Contaminated water in which radioactive material was adsorbed on fine iron powder was measured for the concentration of radioactive material, that is, radioactive iodine (I-131), cesium-137, and cesium-134, and confirmed that the level was below the emission standard. After that, it is discharged into the sea.

  100 g of contaminated water was collected and measured for radioactive iodine (I-131), cesium-137, and cesium-134 using a NaI (TI) scintillation type gamma ray spectrometer EMF211 manufactured by EMF Japan Corporation. As a result, radioactive iodine (I-131) was not detected, but cesium-137 was detected at 556.69 Bq / kg, and cesium-134 was detected at 225.56 Bq / kg. 5 g of iron fine powder was put into 100 g of this contaminated water and stirred, and then rotated at 3000 rpm for 10 minutes with a centrifuge manufactured by Hitachi, Ltd. to separate water and fine powder. The obtained water was taken out and measured by the above apparatus. As a result, radioactive iodine (I-131) was not detected, but cesium-137 was detected at 266.12 Bq / kg, and cesium-134 was detected at 106.10 Bq / kg. . It can be seen that cesium is less than half.

  100 g of contaminated water obtained by washing the contaminated soil was collected, and radioactive iodine (I-131), cesium-137, and cesium-134 were obtained by using a NaI (TI) scintillation type gamma ray spectrometer EMF211 manufactured by EMF Japan Co., Ltd. Was measured. As a result, radioactive iodine (I-131) was not detected, but cesium-137 detected 465.92 Bq / kg and cesium-134 detected 186.66 Bq / kg. 5 g of iron fine powder was put into 100 g of this contaminated water and stirred, and then rotated at 3000 rpm for 10 minutes with a centrifuge manufactured by Hitachi, Ltd. to separate water and fine powder. The obtained water was taken out and measured by the above apparatus. As a result, radioactive iodine (I-131) was not detected, but cesium-137 detected 322.10 Bq / kg and cesium-134 detected 125.05 Bq / kg. .

  Into the water obtained in Example 2, 5 g of new fine iron powder was added, stirred, and then centrifuged in the same manner, and the obtained water component was measured in the same manner. As a result, although radioactive iodine (I-131) was not detected, cesium-137 detected 199.67 Bq / kg and cesium-134 detected 93.20 Bq / kg. It can be seen that cesium is removed stepwise by introducing fine iron powder and repeating the stirring.

Claims (5)

A remover for removing the radioactive substance from the liquid contaminated by the radioactive substance,
A radioactive substance removing agent comprising, as a main component, a fine powder having one or more kinds of particle sizes selected from iron or iron alloy oxides or nitrides.   The radioactive substance removing agent according to claim 1, wherein the particle size of the fine powder is more preferably 10 to 100 nm.   The radioactive substance removing agent according to claim 1 or 2, wherein the fine powder is dust generated by laser welding or laser cutting of iron or an iron alloy in air or nitrogen.   The radioactive substance removing agent according to any one of claims 1 to 3, wherein the radioactive substance is cesium. Preparing the container;
Adding 1 to 30 parts by weight of the radioactive substance removing agent according to any one of claims 1 to 5 to 100 parts by weight of water contaminated by radioactive substances in the container;
Stirring the mixture of water and radioactive substance remover in the container;
Separating the stirred mixture into an iron component and a water component;
Discharging the water component from the container.