Actinoid adsorbent

Abstract

To provide an actinoid adsorbent capable of easily adsorbing actinoid elements in an acidic aqueous solution in one aspect of the present invention.SOLUTION: An actinoid adsorbent for adsorbing actinoid elements contained in an acidic solution, comprising an LTL-type zeolite having a Na2O / Al2O3 molar ratio of 0.1 or more and less than 0.5.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to adsorbents for actinide elements. [Background technology]

[0002] As part of efforts to decommission the Fukushima Daiichi Nuclear Power Plant, efforts are underway to remove the composite solid (fuel debris) that forms when nuclear fuel and other nuclear power plant components, such as metals and concrete, react and melt at high temperatures, then cool and solidify. In addition to the various components of the nuclear power plant, the fuel debris also contains actinide elements such as uranium, which are useful as energy resources. Therefore, efforts are being made to recover these energy-resource elements from the fuel debris and utilize them effectively. One method of recovering actinide elements from fuel debris that has attracted attention is the adsorption and recovery of actinide elements from the solution obtained by dissolving the recovered fuel debris.

[0003] Since fuel debris can only be dissolved by acid dissolution using highly acidic acids such as aqua regia, the resulting solution is acidic. Therefore, to adsorb and recover actinide elements from the solution, an adsorbent capable of adsorbing actinide elements in an acidic solution is desired. Furthermore, lanthanide elements such as europium, dysprosium, and neodymium are known to be substitutes for actinide elements when evaluating the adsorption properties of actinide elements (e.g., Non-Patent Documents 1, 2, and 3). Therefore, an adsorbent capable of adsorbing lanthanide elements in an acidic solution is also desired.

[0004] Patent Document 1 discloses a decontamination agent for radioactive uranium in seawater that uses a commercially available L-type zeolite (UOP-L manufactured by UOP Corporation) (Comparative Examples 1 and 6 in Patent Document 1). In this regard, commercially available L-type zeolites such as UOP-L manufactured by UOP Corporation generally have a potassium cation type counter ion (see "EXPERIMENTAL" and "Materials" in Non-Patent Document 4). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-168349 A [Non-patent literature]

[0006] [Non-Patent Document 1] Journal of Radioanalytical and Nuclear Chemistry, 2022, Vol.331, Issue 12, pages 5851-5858 [Non-patent document 2] Coordination Chemistry Reviews, Vol.318, 2016, pages 131-134 [Non-patent document 3] Journal of Radioanalytical and Nuclear Chemistry, Vol.303, Issue 1, 2015, pages 681-691 [Non-patent document 4] Uptake Selectivity for Different Types of Zeolites in the Presence of Boric Acid(WM2015 Conference,15244,March 15-19,2015) Summary of the Invention [Problem to be solved by the invention]

[0007] Patent Document 1 discloses that commercially available L-type zeolite (UOP-L manufactured by UOP) hardly adsorbs uranium in a uranium-containing solution with an initial pH of 3.2 (Comparative Examples 1 and 6 of Patent Document 1).

[0008] A first object of the present disclosure is to provide an actinide adsorbent that easily adsorbs actinide elements in an acidic aqueous solution.A second object of the present disclosure is to provide a lanthanide adsorbent that easily adsorbs lanthanide elements in an acidic aqueous solution. [Means for solving the problem]

[0009] The present inventors have conducted research into the adsorption of actinide and lanthanide elements in acidic aqueous solutions, focusing on the structure of zeolites and the cation species of zeolites. As a result, they have found that LTL zeolites having a molar ratio of sodium to alumina, calculated as oxide (NaO) (hereinafter also referred to as the "NaO / AlO molar ratio") within a predetermined range, exhibit excellent actinide and lanthanide adsorption properties in acidic aqueous solutions. On the other hand, they have found that commercially available LTL zeolites such as those used in Patent Document 1 generally have a potassium cation type and an NaO / AlO molar ratio outside the aforementioned predetermined range, and therefore hardly adsorb actinide and lanthanide elements in acidic aqueous solutions.

[0010] That is, the present invention is as defined in the claims, and the gist of the present disclosure is as follows: [1] to [6] below correspond to the first invention, and [7] to

[12] below correspond to the second invention. [1] An actinide adsorbent for adsorbing actinide elements contained in an acidic solution, the actinide adsorbent comprising LTL zeolite having a Na2O / Al2O3 molar ratio of 0.1 or more and less than 0.5. [2] The actinide adsorbent according to [1], wherein the K2O / Al2O3 molar ratio of the LTL zeolite is 0.5 or more and less than 1.0. [3] The actinide adsorbent according to [1] or [2], characterized in that the actinide element is one or more elements selected from the group consisting of americium (Am), neptunium (Np), curium (Cm), berkelium (Bk), californium (Cf), and einsteinium (Es). [4] The actinide adsorbent according to any one of [1] to [3] above, wherein the pH of the acidic solution is 1.0 or more and 6.0 or less. [5] A column for separating actinide elements from an acidic solution, the column being packed with the actinide adsorbent according to any one of [1] to [4] above. [6] A method for adsorbing an actinide element, comprising contacting the LTL zeolite contained in the actinide adsorbent according to any one of [1] to [4] above with an acidic solution containing an actinide element. [7] A lanthanoid adsorbent for adsorbing a lanthanoid element contained in an acidic solution, the lanthanoid adsorbent comprising an LTL zeolite having a Na2O / Al2O3 molar ratio of 0.1 or more and less than 0.5. [8] The lanthanoid adsorbent according to [7], wherein the K2O / Al2O3 molar ratio of the LTL zeolite is 0.5 or more and less than 1.0. [9] The lanthanoid adsorbent according to [7] or [8], wherein the lanthanoid element is one or more elements selected from the group consisting of europium, dysprosium, and neodymium.

[10] The lanthanoid adsorbent according to any one of [7] to [9], wherein the pH of the acidic solution is 1.0 or more and 6.0 or less.

[11] A column for separating lanthanoid elements from an acidic solution, the column being packed with the lanthanoid adsorbent according to any one of [7] to

[10] above.

[12] A method for adsorbing a lanthanoid element, comprising contacting the LTL zeolite contained in the lanthanoid adsorbent according to any one of [7] to

[10] above with an acidic solution containing a lanthanoid element. [Effects of the Invention]

[0011] According to the first invention of the present disclosure, an actinide adsorbent exhibiting excellent actinide adsorption properties in an acidic aqueous solution can be provided, and according to the second invention of the present disclosure, a lanthanide adsorbent exhibiting excellent lanthanide adsorption properties in an acidic aqueous solution can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0012] First, the meaning of each term in this specification will be explained.

[0013] In this specification, "zeolite" refers to a compound having a regular structure in which skeleton atoms (hereinafter also referred to as "T atoms") are arranged via oxygen (O), and the T atoms are composed of at least either metal atoms or metalloid atoms. Examples of metal atoms include one or more atoms selected from the group consisting of aluminum (Al), titanium (Ti), iron (Fe), zinc (Zn), gallium (Ga), and tin (Sn), with aluminum being preferred. Examples of metalloid atoms include at least one atom selected from the group consisting of boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), and tellurium (Te), with silicon being preferred.

[0014] "Zeolite-like substances" are compounds that have a regular structure in which T atoms are oxygen-mediated, and in which the T atoms contain at least one atom other than a metal or metalloid. Examples of zeolite-like substances include complex phosphorus compounds containing phosphorus (P) as the T atom, such as aluminophosphate (AlPO) and silicoaluminophosphate (SAPO). "Zeolite-like substances" are distinguished from "zeolites," in which the T atoms are composed solely of at least one of metal atoms and metalloid atoms.

[0015] The "regular structure in which T atoms are oxygen-mediated (hereinafter also referred to as "skeletal structure")" of zeolite and zeolite-like substances is a skeletal structure identified by the structure code (hereinafter also referred to simply as "structure code") established by the Structure Commission of the International Zeolite Association. For example, an "LTL structure" is a skeletal structure identified by the structure code "LTL." The skeletal structure (structure code) of each zeolite can be identified, for example, by comparing it with the XRD pattern (hereinafter also referred to as "reference pattern") of each structure listed on the website of the Structure Commission of the International Zeolite Association, "Zeolite Framework Types at http: / / www.iza-struture.org / databases / ." In this embodiment, the terms skeletal structure, crystalline structure, and crystalline phase are used interchangeably. Note that a zeolite having a skeletal structure identified by the structure code "LTL" is called an LTL zeolite or an L zeolite.

[0016] An "aluminosilicate" is a composite oxide having a structure consisting of a repeating network of aluminum (Al) and silicon (Si) via oxygen (O). In this embodiment, aluminosilicate also includes a structure consisting of a repeating network of aluminum (Al) and silicon (Si) via oxygen (O), in which a portion of the aluminum (e.g., 30% or less of the aluminum as T atoms) is substituted with other metal atoms. Among aluminosilicates, those that have a crystalline XRD peak in their powder X-ray diffraction (hereinafter also referred to as "XRD") pattern are "crystalline aluminosilicates," and those that do not have a crystalline XRD peak are "amorphous aluminosilicates." Note that zeolites whose T atoms are aluminum (Al) and silicon (Si) fall under the category of "crystalline aluminosilicates."

[0017] In this embodiment, the XRD pattern is measured using CuKα radiation as a radiation source, and the measurement conditions include the following. Acceleration current / voltage: 40mA / 40kV Radiation source: CuKα radiation (λ=1.5405Å) Measurement mode: Continuous scan Scan condition: 40° / min Measurement range: 2θ=3° to 43° Divergence vertical limit slit: 10mm Divergence / entrance slit: 1° Receiving slit: open Detector: D / teX Ultra Ni filter used

[0018] The XRD pattern can be measured using a general powder X-ray diffractometer (e.g., Ultima IV Protectus, manufactured by Rigaku Corporation). The crystalline XRD peak is a peak whose peak top 2θ is identified and detected in the analysis of the XRD pattern using general analysis software (e.g., SmartLab Studio II, manufactured by Rigaku Corporation). The following conditions can be used for analyzing the XRD pattern. Fitting conditions: Automatic, refine background Dispersive pseudo-Voigt function (peak shape) Background removal method: Fitting method Kα2 removal method: Kα1 / Kα2 ratio=0.497 Smoothing method: B-Spline curve Smoothing conditions: second-order differential method, σ cut value = 3, χ threshold = 1.5

[0019] The compositions in this embodiment, such as the molar ratio of silica to alumina (hereinafter also referred to as the "SiO2 / Al2O3 molar ratio"), the molar ratio of sodium in terms of oxide (Na2O) to alumina (Na2O / Al2O3 molar ratio), and the molar ratio of potassium in terms of oxide (K2O) to alumina (hereinafter also referred to as the "K2O / Al2O3 molar ratio"), can be measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) using a general ICP apparatus (e.g., OPTIMA5300DV, manufactured by PerkinElmer).

[0020] [First invention] Hereinafter, one embodiment of the first invention according to the present disclosure will be described. This embodiment relates to an actinide adsorbent.

[0021] The actinide adsorbent of this embodiment contains LTL zeolite. The LTL zeolite contained in the actinide adsorbent of this embodiment (hereinafter also referred to as "LTL zeolite of this embodiment") has a Na2O / Al2O3 molar ratio of 0.1 or more and less than 0.5. When the Na2O / Al2O3 molar ratio of the LTL zeolite of this embodiment is 0.1 or more and less than 0.5, actinide elements are easily adsorbed. On the other hand, when the Na2O / Al2O3 molar ratio of the LTL zeolite is outside the range of 0.1 or more and less than 0.5, actinide elements are less easily adsorbed.

[0022] In the LTL zeolite according to this embodiment, the state of sodium (Na) is not particularly limited, and examples thereof include a compound (e.g., an oxide), a metal (element), an ion, an alloy, or two or more of these. From the viewpoint of facilitating adsorption of actinide elements, the state of sodium (Na) contained in the LTL zeolite is preferably an ion.

[0023] In the LTL zeolite according to this embodiment, sodium (Na) is preferably contained in a form in which it is supported on the LTL zeolite, from the viewpoint of facilitating adsorption of actinide elements, and more preferably in a form in which it is supported as a counter ion for compensating for the charge of the framework structure of the LTL zeolite. In this embodiment, "containing a predetermined element" means that the predetermined element is contained in the LTL zeolite, and the predetermined element may be contained in any state and at any site. On the other hand, "supporting a predetermined element" means that the predetermined element is contained in the LTL zeolite as a component other than T atoms. Examples of the supported form of the predetermined element include a form in which the predetermined element is supported on at least one of the outer surface of the zeolite (the surface of the zeolite excluding the inner surfaces of the pores) and the inner surfaces of the pores.

[0024] In the LTL zeolite according to this embodiment, the Na2O / Al2O3 molar ratio may be 0.1 or more and less than 0.5, but from the viewpoint of making it easier for actinide elements to be adsorbed, it is preferably 0.20 or more and 0.45 or less, and more preferably 0.25 or more and 0.40 or less.

[0025] In the LTL zeolite according to this embodiment, the ratio of the mass of sodium in terms of oxide (NaO) to the mass of the LTL zeolite (the total mass of the LTL zeolite according to this embodiment) (hereinafter also referred to as the "NaO content") is not particularly limited, as long as the NaO / AlO molar ratio is 0.1 or more and less than 0.5. From the viewpoint of more easily adsorbing actinide elements, the NaO content is preferably 1.0 mass% or more, more preferably 2.0 mass% or more, and even more preferably 2.5 mass% or more. Furthermore, from the viewpoint of more easily adsorbing actinide elements, the NaO content is preferably 6.0 mass% or less, more preferably 5.5 mass% or less, and even more preferably 5.0 mass% or less. The upper and lower limit values of the NaO content may be any combination of the upper and lower limit values described above. From the viewpoint of making it easier for actinide elements to be adsorbed, the upper and lower limit values are preferably 1.0 mass% or more and 6.0 mass% or less, more preferably 2.0 mass% or more and 5.5 mass% or less, and even more preferably 2.5 mass% or more and 5.0 mass% or less.

[0026] The LTL zeolite according to this embodiment may or may not contain potassium (K). From the viewpoint of facilitating adsorption of actinide elements, the K2O / Al2O3 molar ratio of the LTL zeolite according to this embodiment is preferably less than 1.0, more preferably 0.80 or less, and even more preferably 0.70 or less. From the viewpoint of facilitating adsorption of actinide elements, the K2O / Al2O3 molar ratio is preferably 0.50 or more, more preferably 0.55 or more, and even more preferably 0.60 or more. The K2O / Al2O3 molar ratio may be any combination of the above-mentioned upper and lower limits, but from the viewpoint of facilitating adsorption of actinide elements, it is preferably 0.50 or more but less than 1.0, more preferably 0.55 or more and 0.80 or less, and even more preferably 0.60 or more and 0.70 or less.

[0027] In the LTL zeolite according to this embodiment, the state of potassium (K) is not particularly limited, and examples thereof include a compound (e.g., an oxide), a metal (element), an ion, an alloy, or two or more of these. From the viewpoint of facilitating adsorption of actinide elements, the state of potassium (K) in the LTL zeolite is preferably an ion.

[0028] In the LTL zeolite according to this embodiment, potassium (K) is preferably contained in a form in which it is supported on the LTL zeolite, from the viewpoint of making it easier for the actinide element to be adsorbed, and more preferably in a form in which it is supported as a counter ion for compensating for the charge of the framework structure of the LTL zeolite.

[0029] In the LTL zeolite according to this embodiment, the ratio of the mass of potassium in terms of oxide (KO) to the mass of the LTL zeolite (the total mass of the LTL zeolite according to this embodiment) (hereinafter also referred to as the "KO content") is not particularly limited, but from the viewpoint of facilitating adsorption of actinide elements, it is preferably 14.0 mass% or less, more preferably 13.0 mass% or less, and even more preferably 12.0 mass% or less. Furthermore, from the viewpoint of facilitating adsorption of actinide elements, the KO content is preferably 8.5 mass% or more, more preferably 9.5 mass% or more, and even more preferably 10.0 mass% or more. The upper and lower limits of the KO content may be any combination of the above-mentioned upper and lower limits, but from the viewpoint of facilitating adsorption of actinide elements, it is preferably 8.5 mass% or more and 14.0 mass% or less, more preferably 9.5 mass% or more and 13.0 mass% or less, and even more preferably 10.0 mass% or more and 12.0 mass% or less.

[0030] The SiO2 / Al2O3 molar ratio of the LTL zeolite according to this embodiment is not particularly limited, but from the viewpoint of easier adsorption of actinide elements, it is preferably 2.0 or more, more preferably 3.0 or more, and even more preferably 4.0 or more. Furthermore, from the viewpoint of easier adsorption of actinide elements, the SiO2 / Al2O3 molar ratio of the LTL zeolite according to this embodiment is preferably 6.2 or less, more preferably 6.1 or less, and even more preferably 6.0 or less. The upper and lower limit values of the SiO2 / Al2O3 molar ratio may be any combination of the above-mentioned upper and lower limit values, but from the viewpoint of easier adsorption of actinide elements, it is preferably 2.0 or more and 6.2 or less, more preferably 3.0 or more and 6.1 or less, and even more preferably 4.0 or more and 6.0 or less.

[0031] The T atoms (T atoms constituting the framework structure) of the LTL zeolite according to this embodiment are not particularly limited as long as they are composed of at least either metal atoms or metalloid atoms, but from the viewpoint of facilitating adsorption of actinide elements, they are preferably composed of aluminum (Al) and silicon (Si). In other words, the LTL zeolite according to this embodiment is preferably a crystalline aluminosilicate having an LTL crystal structure.

[0032] Commercially available LTL zeolites may be used as the LTL zeolite according to this embodiment, but commercially available LTL zeolites generally have potassium counter ion cations and a NaO / AlO molar ratio of less than 0.1. Therefore, when using commercially available LTL zeolites (LTL zeolites having a NaO / AlO molar ratio of less than 0.1) as the LTL zeolite according to this embodiment, it is usually necessary to adjust the NaO / AlO molar ratio of the LTL zeolite to 0.1 or more and less than 0.5. To adjust the NaO / AlO molar ratio of the LTL zeolite, for example, an ion exchange treatment can be used in which potassium contained as a counter ion in the LTL zeolite is ion-exchanged with sodium.

[0033] The ion exchange treatment for ion-exchanging potassium for sodium can be performed using a conventionally known method, and is not particularly limited. For example, a method of contacting LTL zeolite with an aqueous solution containing sodium ions (hereinafter also referred to as a "sodium-containing aqueous solution") can be used. By increasing the contact time between the sodium-containing aqueous solution and LTL zeolite or increasing the sodium concentration in the sodium-containing aqueous solution, more potassium can be ion-exchanged for sodium. The contact conditions between the sodium-containing aqueous solution and LTL zeolite can be appropriately set in consideration of these characteristics so that the Na2O / Al2O3 molar ratio of the LTL zeolite is 0.1 or more and less than 0.5. Furthermore, LTL zeolite that has been ion-exchanged can be subjected to another ion exchange treatment. Since more potassium can be ion-exchanged for sodium by increasing the number of ion exchange treatments, the number of ion exchange treatments can be appropriately set so that the Na2O / Al2O3 molar ratio of the LTL zeolite is 0.1 or more and less than 0.5. For example, the number of ion exchange treatments can be set from 1 to 10 times, or even from 1 to 5 times.

[0034] The ion-exchanged LTL zeolite may be subjected to at least one of a washing treatment and a drying treatment. The washing treatment is a treatment for washing the LTL zeolite. For example, the washing treatment may be performed by washing the LTL zeolite with pure water. The drying treatment is a treatment for removing moisture adsorbed on the LTL zeolite. The drying conditions are arbitrary as long as they can remove moisture from the LTL zeolite. One example of the drying conditions is drying the LTL zeolite in an air atmosphere at a temperature of 50°C to 150°C for 10 hours to 24 hours.

[0035] The actinide adsorbent of this embodiment may be the above-mentioned LTL zeolite powder, or may be a compact containing LTL zeolite, which is more likely to improve the adsorption performance of actinide elements. The compact containing LTL zeolite may be composed only of LTL zeolite, or may further contain one or more selected from the group consisting of a binder, a compacting aid, and water.

[0036] The binder may be an organic binder, an inorganic binder, or both. Examples of organic binders include at least one binder selected from the group consisting of polyethylene oxide, hydroxyethyl methylcellulose, starch, corn starch, molasses, lactose, gelatin, dextrin, gum arabic, alginic acid, acrylic acid, polyethylene glycol, and polyvinylpyrrolidone. Examples of inorganic binders include at least one binder selected from the group consisting of clay, silica, alumina, and zirconia. From the viewpoint of more easily adsorbing actinide elements, the binder is preferably at least one binder selected from the group consisting of starch, acrylic acid, clay, silica, alumina, and zirconia, and more preferably clay.

[0037] The content of the binder in the actinide adsorbent of this embodiment can be, for example, 5% by mass or more and 70% by mass or less relative to 100% by mass of the actinide adsorbent.

[0038] Examples of molding aids include water-soluble or water-insoluble celluloses such as one or more selected from the group consisting of carboxylmethylcellulose (hereinafter also referred to as "CMC"), hydroxycellulose, hydroxypropylmethylcellulose, hydroxypropylcellulose, ethylcellulose, and cellulose nanofiber; guar gum derivatives such as at least one of guar gum and hydroxypropylguar gum; polysaccharides such as one or more selected from the group consisting of xanthan gum, welan gum, and gellan gum, which belong to biogums; polyethyleneimine derivatives; polyvinylpyrrolidone (hereinafter also referred to as "PVP"); alcohols such as one or more selected from the group consisting of glycerin, polyvinyl alcohol, and ethylene glycol derivatives; cationic, anionic, or nonionic surfactants; aqueous urethane; and polyacrylic acid derivatives, and these may be used alone or in combination of two or more. The CMC may be sodium carboxymethylcellulose. Preferred molding aids include at least one of CMC and hydroxypropylcellulose.

[0039] The content of the molding aid in the actinide adsorbent of this embodiment can be, for example, 0.1% by mass or more and 10% by mass or less relative to 100% by mass of the actinide adsorbent.

[0040] The water content in the actinide adsorbent of this embodiment can be, for example, 0.1 mass % or more and 40 mass % or less relative to 100 mass % of the actinide adsorbent.

[0041] The actinide adsorbent of this embodiment contains a binder in addition to the LTL zeolite, which makes it easier to mold the actinide adsorbent of this embodiment into a predetermined shape. Furthermore, the actinide adsorbent of this embodiment contains a molding aid and water in addition to the LTL zeolite and binder, which further improves moldability. An actinide adsorbent in the form of a molded body can be produced, for example, by molding a mixture of the LTL zeolite and binder (and optionally a molding aid and water) into a predetermined shape and calcining it. The shape of the molded body is not particularly limited, but may be at least one selected from the group consisting of spherical, approximately spherical, ellipsoidal, cylindrical, polyhedral, and irregular.

[0042] The actinide adsorbent of this embodiment can be used as an adsorbent for adsorbing actinide elements contained in an acidic solution. The actinide adsorbent of this embodiment is preferably used as an adsorbent for adsorbing one or more actinide elements selected from the group consisting of americium (Am), neptunium (Np), curium (Cm), berkelium (Bk), californium (Cf), and einsteinium (Es), and more preferably used as an adsorbent for adsorbing americium (Am).

[0043] The actinide element can be adsorbed by the actinide adsorbent of this embodiment by contacting the LTL zeolite contained in the actinide adsorbent of this embodiment with an acidic solution containing the actinide element (hereinafter referred to as "acidic actinide solution").

[0044] The method for bringing the LTL zeolite according to this embodiment into contact with the acidic actinide solution is not particularly limited, but examples include a method in which the actinide adsorbent according to this embodiment is packed into a reaction tube and the acidic actinide solution is passed through the tube, and a method in which the actinide adsorbent according to this embodiment is immersed in the acidic actinide solution.

[0045] The acidic actinide solution is a solution containing at least an actinide element and a solvent. The actinide element contained in the acidic actinide solution is one or more elements selected from the group consisting of actinium (Ac), thorium (Th), protactinium (Pa), uranium (U), neptunium (Np), plutonium (Pu), americium (Am), curium (Cm), berkelium (Bk), californium (Cf), einsteinium (Es), fermium (Fm), mendelevium (Md), nobelium (No), and lawrencium (Lr). Among these, from the viewpoint of making the actinide element more easily adsorbed, one or more elements selected from the group consisting of americium (Am), neptunium (Np), curium (Cm), berkelium (Bk), californium (Cf), and einsteinium (Es) are preferred, and americium (Am) is more preferred. The solvent contained in the acidic actinide solution may be at least one of water and alcohol, with water being preferred.

[0046] The concentration of the actinide element in the acidic actinide solution can be set appropriately depending on the amount of LTL zeolite to be brought into contact with the acidic actinide solution, and may be, for example, 5 mmol / L or more and 500 mmol / L or less.

[0047] The pH of the acidic actinide solution is less than 7. From the viewpoint of easier adsorption of actinide elements, the pH of the acidic actinide solution is preferably 6.0 or less, more preferably 5.5 or less, and even more preferably 5.0 or less. From the viewpoint of easier adsorption of actinide elements, the pH of the acidic actinide solution is preferably 1.0 or more, more preferably 3.0 or more, and even more preferably 4.0 or more. The upper and lower limit values of the pH of the acidic actinide solution may be any combination of the above-mentioned upper and lower limit values, but from the viewpoint of easier adsorption of actinide elements, the pH is preferably 1.0 or more and 6.0 or less, more preferably 3.0 or more and 5.5 or less, and even more preferably 4.0 or more and 5.0 or less.

[0048] The acidic actinide solution may contain elements other than actinide elements. Examples of other elements that may be contained in the acidic actinide solution include one or more elements selected from the group consisting of cesium (Cs), strontium (Sr), chromium (Cr), zirconium (Zr), molybdenum (Mo), cobalt (Co), iron (Fe), boron (B), silicon (Si), barium (Ba), iodine (I), tellurium (Te), and ruthenium (Ru). A specific example of the acidic actinide solution to be brought into contact with the LTL zeolite according to this embodiment is an acidic fuel debris solution obtained by dissolving fuel debris (a composite solid formed by a high-temperature reaction between nuclear fuel and nuclear power plant constituent materials (metal materials, concrete, etc.) that melt and then cool and solidify) in an acidic solution such as aqua regia. It is preferable that the acidic actinide solution to be brought into contact with the LTL zeolite according to this embodiment does not contain seawater.

[0049] Since the adsorption of actinide elements by the actinide adsorbent of this embodiment proceeds by contacting the LTL zeolite of this embodiment with an acidic actinide solution, the contact conditions are not particularly limited. For example, the contact time between the LTL zeolite of this embodiment and the acidic actinide solution can be 10 hours or more and 24 hours or less, and the contact temperature between the LTL zeolite of this embodiment and the acidic actinide solution can be 10°C or more and 80°C or less.

[0050] Furthermore, the actinide adsorbent of this embodiment can be used as a packing material for a column for separating actinide elements from an acidic actinide solution. When the acidic actinide solution is passed through a column packed with the actinide adsorbent, the LTL zeolite contained in the actinide adsorbent comes into contact with the acidic actinide solution, and the actinide elements are adsorbed onto the actinide adsorbent. As a result, the actinide elements can be separated from the acidic actinide solution.

[0051] The actinide adsorbent of this embodiment described above contains an LTL zeolite having a NaO / AlO molar ratio of 0.1 or more and less than 0.5. LTL zeolite having a NaO / AlO molar ratio of 0.1 or more and less than 0.5 more easily adsorbs actinide elements contained in acidic aqueous solutions than potassium-type LTL zeolite having a NaO / AlO molar ratio of less than 0.1. Therefore, the actinide adsorbent of this embodiment exhibits superior actinide adsorption properties compared to adsorbents using potassium-type LTL zeolite having a NaO / AlO molar ratio of less than 0.1. Although the reason why the actinide adsorbent of this embodiment exhibits excellent actinide adsorption properties is not clear, it is presumed that, because sodium has a smaller ionic radius than potassium, actinide elements have better access to the adsorption sites of actinide elements in LTL zeolite having a Na2O / Al2O3 molar ratio of 0.1 or more and less than 0.5 compared to potassium-type LTL zeolite having a Na2O / Al2O3 molar ratio of less than 0.1, and as a result, actinide elements are more easily adsorbed in an acidic aqueous solution.

[0052] [Second Invention] Next, a second embodiment of the present disclosure will be described, which relates to a lanthanide adsorbent.

[0053] The lanthanoid adsorbent of this embodiment contains an LTL zeolite having a NaO / AlO molar ratio of 0.1 or more and less than 0.5 (hereinafter also referred to as "the LTL zeolite of this embodiment"). The lanthanoid adsorbent of this embodiment is the same as the actinide adsorbent of the first invention except for its different application, and therefore detailed description of aspects other than its application will be omitted.

[0054] The lanthanoid adsorbent of this embodiment can be used as an adsorbent for adsorbing lanthanoid elements contained in an acidic solution. The lanthanoid adsorbent of this embodiment is preferably used as an adsorbent for adsorbing one or more elements selected from the group consisting of europium (Eu), dysprosium (Dy), and neodymium (Nd), and more preferably used as an adsorbent for adsorbing europium (Eu).

[0055] The adsorption of lanthanoid elements by the lanthanoid adsorbent of this embodiment can be carried out by contacting the LTL zeolite of this embodiment with an acidic solution containing lanthanoid elements (hereinafter also referred to as "acidic lanthanoid solution").

[0056] The method of contacting the LTL zeolite with the acidic lanthanoid solution according to this embodiment is the same as the method of contacting the LTL zeolite with the acidic actinoid solution according to the first invention, except that an acidic lanthanoid solution is used instead of the acidic actinoid solution, and therefore detailed explanations other than the acidic lanthanoid solution will be omitted.

[0057] The acidic lanthanide solution is the same as the acidic actinide solution of the first invention, except that a lanthanide element is used instead of the actinide element. The lanthanide element contained in the acidic lanthanide solution is one or more elements selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). Among these, from the viewpoint of facilitating adsorption of the lanthanide element, one or more elements selected from the group consisting of europium (Eu), dysprosium (Dy), and neodymium (Nd) are preferred.

[0058] The lanthanoid adsorbent of this embodiment can also be used as a packing material for a column for separating lanthanoid elements from an acidic lanthanoid solution. When an acidic lanthanoid solution is passed through a column packed with the lanthanoid adsorbent, the LTL zeolite contained in the lanthanoid adsorbent comes into contact with the acidic lanthanoid solution, and the lanthanoid elements are adsorbed onto the lanthanoid adsorbent. As a result, the lanthanoid elements can be separated from the acidic lanthanoid solution.

[0059] The lanthanoid adsorbent of this embodiment preferably has an adsorption distribution coefficient of the lanthanoid element in an acidic solution of more than 50 mL / g, more preferably 60 mL / g or more, and even more preferably 70 mL / g or more. The upper limit of the adsorption distribution coefficient of the lanthanoid element in an acidic solution is not particularly limited, but may be, for example, 1.0 × 10 4 In other words, the lanthanoid adsorbent of the present embodiment has an adsorption distribution coefficient of a lanthanoid element in an acidic solution of more than 50 mL / g and less than 1.0 × 10 4 mL / g or less is preferable, and 60 mL / g or more and 1.0 × 10 4 mL / g or less is more preferable, and 70 mL / g or more and 1.0 × 10 4It is particularly preferable that the concentration is mL / g or less.

[0060] Here, the "adsorption distribution coefficient" is a value that indicates the adsorption characteristics of an adsorbent when the adsorbent is brought into contact with a metal ion-containing aqueous solution (e.g., a lanthanoid ion-containing aqueous solution) to perform an adsorption treatment to adsorb the metal ions, and can be calculated using the following formula (1). Kd = (C - C) / C × V / m (1) Kd: partition coefficient (mL / g) C: Metal ion concentration (ppm) in the metal ion-containing aqueous solution before adsorption treatment C: Metal ion concentration (ppm) in the metal ion-containing aqueous solution at adsorption equilibrium V: Volume of the metal ion-containing aqueous solution used for adsorption treatment (mL) m: Weight of adsorbent used in adsorption treatment (g)

[0061] In the above formula (1), C (the metal ion concentration in the metal ion-containing aqueous solution at adsorption equilibrium) can be the metal ion concentration (ppm) in the metal ion-containing aqueous solution 24 hours or more after the start of the adsorption treatment. The adsorption treatment used to determine the adsorption distribution coefficient can be, for example, a process in which an adsorbent and a metal ion-containing aqueous solution with a metal ion concentration of 10 mmol / L are mixed in a mass ratio of 1:75 (adsorbent:metal ion-containing aqueous solution) and stirred at 25°C for 24 hours or more.

[0062] The lanthanoid adsorbent of the present embodiment described above contains an LTL zeolite having a NaO / AlO molar ratio of 0.1 or more and less than 0.5. LTL zeolite having a NaO / AlO molar ratio of 0.1 or more and less than 0.5 is more likely to adsorb lanthanoid elements contained in acidic aqueous solutions than potassium-type LTL zeolite having a NaO / AlO molar ratio of less than 0.1. For this reason, the lanthanoid adsorbent of the present embodiment exhibits superior lanthanoid adsorption properties compared to adsorbents using potassium-type LTL zeolite having a NaO / AlO molar ratio of less than 0.1. Although the reason why the lanthanoid adsorbent of this embodiment exhibits excellent lanthanoid adsorption properties is not clear, it is presumed that, because sodium has a smaller ionic radius than potassium, lanthanoid elements have better access to the adsorption sites of lanthanoid elements in LTL zeolite having a NaO / AlO molar ratio of 0.1 or more and less than 0.5 compared to potassium-type LTL zeolite having a NaO / AlO molar ratio of less than 0.1, and as a result, lanthanoid elements are more easily adsorbed in acidic aqueous solutions. [Example]

[0063] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples.

[0064] <Crystal structure identification> The samples were subjected to XRD measurement using a general powder X-ray diffractometer (device name: Ultima IV Protectus, manufactured by Rigaku Corporation) under the following measurement conditions: Acceleration current / voltage: 40mA / 40kV Radiation source: CuKα radiation (λ=1.5405Å) Measurement mode: Continuous scan Scan condition: 40° / min Measurement range: 2θ=3° to 43° Divergence vertical limit slit: 10mm Divergence / entrance slit: 1° Receiving slit: open Detector: D / teX Ultra Ni filter used

[0065] The obtained XRD pattern was analyzed using the analysis software attached to the device (software name: Smart Lab Studio II, manufactured by Rigaku Corporation) under the following conditions. Fitting conditions: Automatic, refine background Dispersive pseudo-Voigt function (peak shape) Background removal method: Fitting method Kα2 removal method: Kα1 / Kα2 ratio=0.497 Smoothing method: B-Spline smoothing Smoothing conditions: second-order differential method, σ cut value = 3, χ threshold = 1.5

[0066] The crystal structure of the sample was identified by comparing the obtained XRD pattern with a reference pattern.

[0067] <Composition analysis> For composition analysis, a sample solution was prepared by dissolving the sample in a mixed aqueous solution of hydrofluoric acid and nitric acid. The sample solution was measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) using a standard ICP instrument (instrument name: OPTIMA 5300DV, manufactured by PerkinElmer). The SiO2 / Al2O3 molar ratio, Na2O / Al2O3 molar ratio, and K2O / Al2O3 molar ratio were calculated from the measured values of Si, Al, Na, and K. The Na2O and K2O contents of the sample were also calculated from the measured values of Na and K and the mass of the dissolved sample (total mass of dissolved zeolite).

[0068] <Adsorption distribution coefficient> The adsorption distribution coefficient was calculated from the following formula (2). Kd = (C. - C) / C × V / m (2) Kd: Adsorption distribution coefficient (mL / g) C: Metal ion concentration (ppm) in the simulated solution before adsorption treatment C: Metal ion concentration in the simulated solution after adsorption treatment (ppm) V: Volume of the simulated solution used for adsorption treatment (mL) m: Weight of adsorbent used in adsorption treatment (g)

[0069] Example 1 LTL zeolite (product name: HSZ (registered trademark)-500KOA, manufactured by Tosoh Corporation, SiO / AlO molar ratio: 5.9, NaO / AlO molar ratio: 0.021, KO / AlO molar ratio: 1.1, NaO content: 0.2 mass%, KO content: 18.8 mass%, aluminosilicate) was mixed with 10 times its mass of water and then filtered to produce a cake. A 10-fold mass of aqueous sodium chloride solution (NaCl concentration: 20 mass%) was passed through the LTL zeolite cake, and then a further 10-fold mass of water was passed through. This circulation operation was repeated three times in total, and the resulting cake was then dried at 110°C in the air for 20 hours to obtain an adsorbent of this example consisting of LTL zeolite (SiO / AlO molar ratio: 5.9, NaO / AlO molar ratio: 0.37, KO / AlO molar ratio: 0.67, NaO content: 4.3% by mass, KO content: 11.6% by mass, aluminosilicate).

[0070] Example 2 The adsorbent of this example, consisting of LTL zeolite (SiO / AlO molar ratio: 5.9, NaO / AlO molar ratio: 0.33, KO / AlO molar ratio: 0.71, NaO content: 3.7 mass%, KO content: 12.4 mass%, aluminosilicate), was obtained in the same manner as in Example 1, except that the circulation operation was carried out once.

[0071] Example 3 An adsorbent of this example consisting of LTL zeolite (SiO / AlO molar ratio: 5.9, NaO / AlO molar ratio: 0.25, KO / AlO molar ratio: 0.79, NaO content: 2.8 mass%, KO content: 13.6 mass%, aluminosilicate) was obtained in the same manner as in Example 1, except that an aqueous sodium chloride solution (NaCl concentration: 5 mass%) was used instead of an aqueous sodium chloride solution (NaCl concentration: 20 mass%) and the circulation operation was performed once.

[0072] Comparative Example 1 LTL-type zeolite (product name: HSZ (registered trademark)-500KOA: manufactured by Tosoh Corporation, SiO / AlO molar ratio: 5.9, NaO / AlO molar ratio: 0.021, KO / AlO molar ratio: 1.1, NaO content: 0.2 mass%, KO content: 18.8 mass%, aluminosilicate) was used as the adsorbent in this comparative example.

[0073] Comparative Example 2 LTL zeolite (product name: HSZ (registered trademark)-500KOA, SiO2 / Al2O3 molar ratio: 5.9, Na2O / Al2O3 molar ratio: 0.021, K2O / Al2O3 molar ratio: 1.1, Na2O content: 0.2 mass%, K2O content: 18.8 mass%, aluminosilicate) was mixed with 10 times its mass of water and then filtered to produce a cake. A 10-fold mass of aqueous ammonium chloride solution (ammonium chloride concentration: 20 mass%) was passed through the resulting cake, and then a 10-fold mass of water was passed through once. The resulting cake was then dried at 110°C in an air atmosphere for 20 hours to obtain an adsorbent of this comparative example consisting of LTL zeolite (SiO / AlO molar ratio: 5.8, NaO / AlO molar ratio: 0, KO / AlO molar ratio: 0.37, NaO content: 0.0 mass%, KO content: 7.15 mass%, aluminosilicate).

[0074] Comparative Example 3 MOR-type zeolite (product name: HSZ (registered trademark)-642NAA: manufactured by Tosoh Corporation, SiO / AlO molar ratio: 18.7, NaO / AlO molar ratio: 1.03, KO / AlO molar ratio: 0, NaO content: 5.0 mass%, KO content: 0 mass%, aluminosilicate) was used as the adsorbent in this comparative example.

[0075] <Adsorption evaluation 1> Simulation solutions A1 to C1 were prepared as simulated fuel debris dissolution solutions. Simulation solutions A1 to C1 were obtained by mixing a metal ion-containing reagent, nitric acid, and pure water. Simulation solutions A1 to C1 were each mixed with the metal ion-containing reagent shown below to contain different metal ions. The obtained simulation solutions A1 to C1 all had a metal ion concentration of 10 mmol / L and a pH of 5. Adsorption evaluation was performed using the obtained simulation solutions A1 to C1. [Metal ion-containing reagents] Simulation solution A1: Dy(III); dysprosium nitrate hexahydrate 99.5% (Wako Pure Chemical Industries, Ltd.) Simulated solution B1: Eu(III); europium(III) nitrate hexahydrate (manufactured by Kanto Kagaku Co., Ltd.) Simulation solution C1: Nd(III); neodymium nitrate hexahydrate (Kanto Chemical Co., Ltd.)

[0076] The adsorbents of the Examples and Comparative Examples were mixed with the simulated solutions A1 to C1 at a solid-liquid ratio of 1:75 (solid (g):liquid (g)), and the mixture was sealed in glass screw cap bottles. The glass screw cap bottles were stirred at 25°C for 24 hours using a roller shaker (product name: FLMX-T6-S, manufactured by AS ONE) to carry out an adsorption treatment. After that, solid-liquid separation was carried out using a syringe filter, and the simulated solutions A1 to C1 were collected, respectively.

[0077] The metal ion concentrations of the simulated solutions A1 to C1 before and after the adsorption treatment were measured using a polarized Zeeman atomic absorption spectrophotometer (product name: ZA-2300, manufactured by Hitachi High-Tech Science Corporation) under the following conditions. Using the measured metal ion concentrations before and after the adsorption treatment, the adsorption distribution coefficients of the adsorbents of the examples and comparative examples were calculated from the above formula (2). Photometry: Double beam photometry Atomization method: Air-acetylene flame method Background correction: Polarized Zeeman correction method

[0078] The adsorption distribution coefficients (adsorption distribution coefficients in a simulated solution of pH 5) of the adsorbents of the Examples and Comparative Examples are shown in Table 1 below. [Table 1]

[0079] As shown in Table 1 above, the adsorbents of the Examples had higher adsorption distribution coefficients than the adsorbents of the Comparative Examples for all elements, europium (Eu), dysprosium (Dy), and neodymium (Nd). From these results, it was understood that the adsorbents of the Examples had higher adsorption performance for europium (Eu), dysprosium (Dy), and neodymium (Nd) in an acidic solution of pH 5 than the adsorbents of the Comparative Examples.

[0080] Furthermore, as shown in Non-Patent Documents 1 to 3, it is common general technical knowledge that europium (Eu), dysprosium (Dy), and neodymium (Nd) can be used as substitute elements when evaluating the adsorption performance for actinide elements. Considering this common technical knowledge and the results in Table 1 above (the adsorbents of the Examples have higher adsorption performance for europium, dysprosium, and neodymium in an acidic solution of pH 5 than the adsorbents of the Comparative Examples), it was understood that the adsorbents of the Examples have higher adsorption performance for actinide elements in an acidic solution of pH 5 than the adsorbents of the Comparative Examples.

[0081] <Adsorption evaluation 2> Simulation solutions A1 to C1 were obtained in the same manner as in Adsorption Evaluation 1, except that the mixed amounts of the metal ion-containing reagent, nitric acid, and water were adjusted to a pH of 4. The simulation solutions A1 to C1 with a pH of 4 were designated simulation solutions A2 to C2, respectively. The metal ion concentrations of all simulation solutions A2 to C2 were 10 mmol / L. The adsorption distribution coefficients of the adsorbents of Example 1 and Comparative Examples 1 and 3 (adsorption distribution coefficients in the simulation solution of pH 4) were determined in the same manner as in Adsorption Evaluation 1, except that simulation solutions A2 to C2 were used instead of simulation solutions A1 to C1, and that adsorption treatment was performed using the adsorbents of Example 1 and Comparative Examples 1 and 3. The results are shown in Table 2.

[0082] [Table 2]

[0083] As shown in Table 2 above, for all of the elements europium (Eu), dysprosium (Dy), and neodymium (Nd), the adsorbent of Example 1 had a higher adsorption distribution coefficient than the adsorbents of Comparative Examples 1 and 3. From this result, it was understood that the adsorbent of Example 1 has higher adsorption performance for europium (Eu), dysprosium (Dy), and neodymium (Nd) in an acidic solution of pH 4 than the adsorbents of Comparative Examples 1 and 3.

[0084] Furthermore, taking into consideration the above-mentioned common technical knowledge (europium, dysprosium, and neodymium are substitute elements for evaluating the adsorption performance for actinide elements) and the results in Table 2 above (the adsorbent of Example 1 has higher adsorption performance for europium, dysprosium, and neodymium in an acidic solution of pH 4 than the adsorbents of Comparative Examples 1 and 3), it was understood that the adsorbent of Example 1 has higher adsorption performance for actinide elements in an acidic solution of pH 4 than the adsorbents of Comparative Examples 1 and 3.

[0085] <Adsorption evaluation 3> Simulation solutions A1 to C1 were obtained in the same manner as in Adsorption Evaluation 1, except that the mixed amounts of the metal ion-containing reagent, nitric acid, and water were adjusted to a pH of 3. The simulation solutions A1 to C1 with a pH of 3 were designated simulation solutions A3 to C3, respectively. The metal ion concentrations of all simulation solutions A3 to C3 were 10 mmol / L. The adsorption distribution coefficients of the adsorbents of Example 1 and Comparative Examples 1 and 3 (adsorption distribution coefficients in the simulation solution with a pH of 3) were determined in the same manner as in Adsorption Evaluation 1, except that simulation solutions A3 to C3 were used instead of simulation solutions A1 to C1, and that adsorption treatment was performed using the adsorbents of Example 1 and Comparative Examples 1 and 3. The results are shown in Table 3.

[0086] [Table 3]

[0087] As shown in Table 3 above, for all of the elements europium (Eu), dysprosium (Dy), and neodymium (Nd), the adsorbent of Example 1 had a higher adsorption distribution coefficient than the adsorbents of Comparative Examples 1 and 3. From these results, it was understood that the actinide adsorbent of Example 1 has higher adsorption performance for europium (Eu), dysprosium (Dy), and neodymium (Nd) in an acidic solution of pH 3 than the actinide adsorbents of Comparative Examples 1 and 3.

[0088] Furthermore, taking into consideration the above-mentioned common technical knowledge (europium, dysprosium, and neodymium are substitute elements for evaluating the adsorption performance for actinide elements) and the results in Table 3 above (the adsorbent of Example 1 has higher adsorption performance for europium, dysprosium, and neodymium in an acidic solution of pH 3 than the adsorbents of Comparative Examples 1 and 3), it was understood that the adsorbent of Example 1 has higher adsorption performance for actinide elements in an acidic solution of pH 3 than the adsorbents of Comparative Examples 1 and 3.

Claims

1. An actinide adsorbent for adsorbing an actinide element contained in an acidic solution, comprising: Na ２ O / Al ２ O ３ An actinide adsorbent comprising an LTL-type zeolite having a molar ratio of 0.1 or more and less than 0.

5.

2. The LTL type zeolite K ２ O / Al ２ O ３ The actinide adsorbent according to claim 1 , wherein the molar ratio is equal to or greater than 0.5 and less than 1.

0.

3. 2. The actinide adsorbent according to claim 1, wherein the actinide element is one or more elements selected from the group consisting of americium (Am), neptunium (Np), curium (Cm), berkelium (Bk), californium (Cf), and einsteinium (Es).

4. 2. The actinide adsorbent according to claim 1, wherein the pH of the acidic solution is 1.0 or more and 6.0 or less.

5. 1. A column for separating actinide elements from an acidic solution, comprising: A column packed with the actinide adsorbent according to any one of claims 1 to 4.

6. A method for adsorbing an actinide element, comprising contacting the LTL zeolite contained in the actinide adsorbent according to any one of claims 1 to 4 with an acidic solution containing an actinide element.

7. A lanthanoid adsorbent for adsorbing a lanthanoid element contained in an acidic solution, comprising: Na ２ O / Al ２ O ３ A lanthanoid adsorbent comprising an LTL-type zeolite having a molar ratio of 0.1 or more and less than 0.

5.

8. The LTL type zeolite K ２ O / Al ２ O ３ The lanthanide adsorbent according to claim 7 , wherein the molar ratio is 0.5 or more and less than 1.

0.

9. 8. The lanthanoid adsorbent according to claim 7, wherein the lanthanoid element is one or more elements selected from the group consisting of europium, dysprosium, and neodymium.

10. 8. The lanthanoid adsorbent according to claim 7, wherein the pH of the acidic solution is 1.0 or more and 6.0 or less.

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