WO2013176956A2 - Sintered product, metal ion adsorbent, method for removing metal ions, and metal ion removing equipment - Google Patents

Sintered product, metal ion adsorbent, method for removing metal ions, and metal ion removing equipment Download PDF

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Publication number
WO2013176956A2
WO2013176956A2 PCT/US2013/041341 US2013041341W WO2013176956A2 WO 2013176956 A2 WO2013176956 A2 WO 2013176956A2 US 2013041341 W US2013041341 W US 2013041341W WO 2013176956 A2 WO2013176956 A2 WO 2013176956A2
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sintered product
metal ion
adsorbent
metal
alkali metal
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PCT/US2013/041341
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French (fr)
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WO2013176956A3 (en
Inventor
Yuji Hiroshige
Toshihiro Kasai
Hiroaki Yamaguchi
Seiichi Ota
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3M Innovative Properties Company
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Publication of WO2013176956A2 publication Critical patent/WO2013176956A2/en
Publication of WO2013176956A3 publication Critical patent/WO2013176956A3/en

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C01G23/003—Titanates
    • C01G23/005—Alkali titanates
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/04—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising compounds of alkali metals, alkaline earth metals or magnesium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/06—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising oxides or hydroxides of metals not provided for in group B01J20/04
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • B01J20/28002—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their physical properties
    • B01J20/28004—Sorbent size or size distribution, e.g. particle size
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30—Processes for preparing, regenerating, or reactivating
    • B01J20/3035—Compressing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30—Processes for preparing, regenerating, or reactivating
    • B01J20/3078—Thermal treatment, e.g. calcining or pyrolizing
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
    • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
    • G21F9/04—Treating liquids
    • G21F9/06—Processing
    • G21F9/12—Processing by absorption; by adsorption; by ion-exchange
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2220/00—Aspects relating to sorbent materials
    • B01J2220/50—Aspects relating to the use of sorbent or filter aid materials
    • B01J2220/58—Use in a single column
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/16—Pore diameter

Definitions

  • the present invention relates to a sintered product, a metal ion adsorbent using the sintered product, a method for removing metal ions using the metal ion adsorbent, and metal ion removing equipment.
  • Patent Document 2 discloses a strontium ion fixative containing a hydrous complex oxide expressed by the general formula:
  • Ce(HP0 4 )x-yH 2 0 (where x is a number in a range from 1.8 to 2.1 , and y is a number in a range from 1 to 4).
  • Patent Document 3 discloses a sodium titanate ion exchanger containing granules having a particle size of 0.1 to 2 mm, wherein a molar ratio of sodium to titanium is 0.6 or lower, a selectivity coefficient of exchange of Na to Sr is 50,000 or higher, an ion exchange capacity is 4.5 meq/g or higher, and a distribution coefficient of radioactive strontium measured in a pH 1 1, 2.0 M NaCl aqueous solution is 40,000 ml/g or higher.
  • Patent Document 1 Japanese Unexamined Patent Application Publication No.
  • Patent Document 2 Japanese Patent No. 2535783
  • Patent Document 3 Japanese Patent No. 4428541
  • An adsorbent for removing radioactive nuclides is used, for example, being filled in an adsorption tower. Effluent is passed into the adsorption tower filled with the adsorbent and the effluent is brought into contact with the adsorbent, whereby radioactive nuclides in the effluent are adsorbed to the adsorbent.
  • an adsorbent In the case in which an adsorbent is used on an industrial scale, it is desirable that the granules be provided in a shape suitable for use in an adsorption tower, and the granules must have adequate mechanical strength.
  • the adsorbent When the mechanical strength is insufficient, the adsorbent may be crushed into fine powder during passage and the fine powder may leak out to a latter stage from the adsorption tower. Because the fine powder leaking out is radioactive waste containing adsorbed radioactive nuclides, the fine powder must be removed by filtering or other treatment, and this is linked to lowering of operating efficiency. Moreover, transport using water flow, or the like, may be performed in order to extract spent adsorbent from the adsorption tower for the purpose of removing radioactive nuclides, but if the adsorbent is brittle, it may be crushed into fine powder by the water pressure, and there is a risk that the fine powder might clog piping.
  • Alkali titanate compounds are known as adsorbents for the purpose of removing strontium, but considering the purpose of removal of radioactive strontium and the use on an industrial scale, it is difficult to obtain a material that has sufficient radiation resistance and can be prepared into a particulate form suitable for column filling.
  • Japanese Patent No. 4428541 is there disclosed an ion exchanger of titanate in particulate form.
  • titanium oxide and an alkali agent are reacted, and the reaction solution is subjected to washing, drying, and crushing to obtain granules of ion exchanger.
  • the strength of the granules is weak, in the case in which the granules are transported using water flow in piping, a portion of the granules may be crushed by the water pressure, and as a result, the crushed granules may clog the piping.
  • One aspect of the present invention relates to a sintered product from sintering a mixture containing a hydrous titanium oxide and an alkali metal compound.
  • the sintered product has excellent metal ion adsorbing ability, and also has sufficient mechanical strength, and the production of fine powder is sufficiently suppressed in the use as an adsorbent.
  • the reason why such effect is produced is thought to be that the alkali metal compound acts as a binding agent during sintering and improves the mechanical strength of the sintered product.
  • the alkali metal compound may include an alkali metal nitrate. Moreover, when the alkali metal compound includes an alkali metal nitrate, the pore density of the sintered product is improved, and the metal ion adsorbing ability of the sintered product is further improved. The reason why such effect is produced is thought to be that a gas produced as a product of degradation of nitrate ions produces pores in the sintered product during sintering.
  • a molar ratio Ci/C 2 of a content d of titanium element to a content C 2 of alkali metal element in the mixture is preferably from 0.5 to 5.0.
  • a sintered product having even more excellent metal ion adsorbing ability is obtained.
  • the sintered product is preferably obtained by sintering the mixture at 100°C or higher, and preferably at from 200 to 600°C or higher.
  • the sintering temperature is less than 100°C, the binding effect of the alkali metal compound may not be obtained sufficiently; when the sintering temperature exceeds 600°C, a portion of the sintered product may crystallize and the metal ion adsorbing ability may be degraded. That is, by setting the sintering temperature to within the abovementioned range, the effect of the alkali metal compound as a binding agent can be obtained more effectively while suppressing crystallization of the sintered product, and both the metal ion adsorbing ability and the mechanical strength can be further improved.
  • the sintered product is preferably porous, and a mean pore size is preferably from 0.1 to 10 ⁇ . Such sintered product becomes even more excellent in metal ion adsorbing ability.
  • the sintered product may be composed of an aggregate of particles including an alkali titanate compound (hereinafter referred to in some cases as “alkali titanate particles”) expressed by A 2 Ti n 0 2 n+i (wherein A denotes an alkali metal, and n denotes from 0.5 to 5.0).
  • alkali titanate particles an alkali titanate compound expressed by A 2 Ti n 0 2 n+i (wherein A denotes an alkali metal, and n denotes from 0.5 to 5.0).
  • the sintered product from sintering a mixture containing a hydrous titanium oxide and an alkali metal compound can be obtained as an aggregate of alkali titanate particles. Note that although there may be cases in which aggregate forms of inorganic particles are obtained even with conventional adsorbents, it was conventionally difficult to suppress the production of fine powder due to dispersing of the inorganic particles. In contrast, with the sintered product of the present embodiment, the cohesive strength between particles is strong, and the production of fine powder is sufficiently suppressed even in the case in which the sintered product is used as an adsorbent.
  • a mean particle size of the alkali titanate particles is preferably from 0.1 to 10 ⁇ .
  • the mean particle size is within the abovementioned range, the metal ion adsorbing ability of the sintered product is further improved.
  • Another aspect of the present invention relates to a metal ion adsorbent containing the above-described sintered product.
  • the metal ion adsorbent contains the above-described sintered product, it has excellent metal ion adsorbing ability. Moreover, according to this metal ion adsorbent, because leakage of fine powder to the outside of the adsorption tower is suppressed and the load of filtering or other treatment at a latter stage from the adsorption tower is reduced, improvement of operating efficiency can be achieved.
  • another aspect of the present invention relates to a method for removing metal ions, including a step in which a treatment solution containing metal ions is brought into contact with the metal ion adsorbent and at least a portion of the metal ions is removed from the treatment solution.
  • Another aspect of the present invention relates to metal ion removing equipment, including a filled tower filled with the metal ion adsorbent.
  • a sintered product can be provided that has excellent metal ion adsorbing ability and can sufficiently suppress production of fine powder in use as an adsorbent, as well as a metal ion adsorbent containing that sintered product.
  • a method can be provided for removing metal ions using the metal ion adsorbent, as well as metal ion removing equipment.
  • FIG. 1 is a schematic illustration of one embodiment of the metal ion removing equipment according to the present invention.
  • FIG. 2 is an illustration of results of SEM observation of the sintered product of Working Example 1.
  • FIG. 3 is an illustration of results of SEM observation of the sintered product of Working Example 2.
  • the sintered product according to the present embodiment is a sintered product from sintering a mixture containing a hydrous titanium oxide and an alkali metal compound, and has excellent metal ion adsorbing ability. Moreover, the sintered product has sufficient mechanical strength, and can sufficiently suppress production of fine powder in use as an adsorbent. The reason why such effect is produced is thought to be that the alkali metal compound acts as a binding agent during sintering and improves the mechanical strength of the sintered product.
  • Sintering is a phenomenon in which, in general, an aggregate of solid powder is hardened by being heated to a melting temperature or lower, or to a temperature at which a partial liquid phase occurs, and a so-called "sintered body," which is a dense solid having great strength, is produced.
  • the driving force of sintering is a force that acts to minimize the surface energy in a system composed of a particle aggregate; by application of the energy, material movement is caused between particles by solid diffusion or melting, and cohesion is brought about.
  • the sintered product according to the present embodiment is sintered by dissolution or solid diffusion of the alkali metal compound in the abovementioned mixture. Moreover, in the sintered product according to the present embodiment, it is thought that the alkali metal moves into the hydrous titanium oxide and an alkali titanate compound is produced. Moreover, in the case in which the alkali metal compound is an alkali metal nitrate, nitric acid gas is furthermore produced by thermolysis of the nitrate, and the sintered product becomes porous.
  • the hydrous titanium oxide is a compound expressed by Ti0 2 -nH 2 0, and can also be referred to as a "hydrate of titanium dioxide.”
  • the method for obtaining the hydrous titanium oxide is not particularly limited; for example, it can be obtained by hydrolysis of titanium tetrachloride.
  • alkali metals include lithium, sodium, potassium, rubidium, and cesium, and among these, lithium, sodium, and potassium are preferred.
  • alkali metal compounds include alkali metal hydroxides and alkali metal salts, and examples of alkali metal salts include alkali metal nitrates.
  • a preferred alkali metal compound is one having a melting point in a range of 200 to 600°C.
  • Such alkali metal compound melts at an optimal sintering temperature to be described, and the effect as an adsorbent can be produced effectively.
  • the melting point of sodium nitrate is 306°C
  • the melting point of potassium nitrate is 339°C
  • the melting point of sodium hydroxide is 328°C
  • the melting point of potassium hydroxide is 360°C
  • the alkali metal compound more preferably includes an alkali metal nitrate.
  • the alkali metal compound includes an alkali metal nitrate
  • the pore density of the sintered product increases, and the metal ion adsorbing ability of the sintered product tends to be further improved.
  • the reason why such effect is produced is thought to be that pores are produced in the sintered product by a gas produced as a product of degradation of nitrate ions.
  • the mixture ratio of the hydrous titanium oxide and the alkali metal compound is preferably adjusted so that, for example, a molar ratio Ci/C 2 of a content Q of titanium element to a content C 2 of alkali metal element becomes from 0.5 to 5.0.
  • the sintered product is composed of an aggregate of particles including an alkali titanate compound (hereinafter referred to in some cases as
  • alkali titanate particles expressed by A 2 Ti n 0 2n+ i (wherein A denotes an alkali metal, and n denotes from 0.5 to 5.0). [0036]
  • the n of the alkali titanate compound can be adjusted by changing the above- described molar ratio Ci/C 2 .
  • the A originates in the alkali metal compound, and the alkali metal denoted by A may be a single kind or a plurality of kinds.
  • a mean particle size of the alkali titanate particles is preferably from 0.1 to
  • the metal ion adsorbing ability of the sintered product tends to be further improved.
  • the mean particle size of the alkali titanate particles is measured by the following method.
  • the maximum diameters in a fixed direction of any 100 alkali titanate particles are measured using an image obtained by surface observation by scanning electron microscope (hereinafter referred to in some cases as "SEM observation"), and the arithmetic mean thereof is taken as the mean particle size of the alkali titanate particles.
  • the sintered product is porous, and a mean pore size is preferably from 0.5 to 5 ⁇ . Such sintered product is even more excellent in metal ion adsorbing ability.
  • the pores of the sintered product are not necessarily in the form of closed cells such that the mean pore size can be measured; for example, the sintered product may be porous in a form having a large number of minute gaps between alkali titanate particles (open cells).
  • the mean pore size of the sintered product is measured by the following method.
  • the maximum diameters in a fixed direction of any 100 pores is measured using an image obtained by SEM observation of the sintered product, and the arithmetic mean thereof is taken as the mean pore size.
  • the form of primary particles constituting the alkali titanate particles is thought to be any of amorphous particles, nano-size crystalline particles, or semicrystal with mixed nano-size crystalline particles and amorphous particles.
  • the sintered product can be prepared, for example, by the following method.
  • an alkali metal compound is added to a slurry of hydrous titanium oxide suspended in a solvent (for example, water).
  • a solvent for example, water
  • the solvent is removed from the slurry by drying and the solid portion is obtained, which is a mixture of hydrous titanium oxide and alkali metal compound.
  • the sintered product is obtained by sintering the solid portion at from 200 to 600°C.
  • the solid portion which is a mixture of hydrous titanium oxide and alkali metal compound, aggregates by compression bonding during removal of the solvent by drying.
  • the aggregated solid portion may be supplied as such to sintering, or may be supplied to sintering after compression molding.
  • Removal of the solvent by drying can be performed, for example, by heating to a temperature of 60 to 95°C. Moreover, removal of the solvent by drying can be performed under normal pressure or can be performed under reduced pressure.
  • the sintering time is not particularly limited, but, for example, can be from 1 to 10 hours.
  • the mean particle size of the alkali titanate particles can be adjusted by changing the particle size of the hydrous titanium oxide in the slurry.
  • alkali titanate particles having a small mean particle size can be obtained by reducing the particle size of the hydrous titanium oxide in the slurry.
  • the sintered product may be used as such as a metal ion adsorbent, or may be used upon crushing to a size adapted for the use.
  • the sintered product in use as an adsorbent to be filled in an adsorption tower, is preferably used in granular form, and the particle size of the granules is preferably from 0.01 to 5 mm, and more preferably from 0.2 to 2 mm.
  • the metal ion adsorbent according to the present embodiment contains the sintered product. Because the metal ion adsorbent according to the present embodiment contains the sintered product, it has excellent metal ion adsorbing ability.
  • the adsorbent is used for removing radioactive nuclides (for example, cesium, strontium, or the like) from effluent in nuclear reactors, nuclear fuel reprocessing plants, and the like
  • radioactive nuclides for example, cesium, strontium, or the like
  • the metal ion adsorbent according to the present embodiment because this leakage of fine powder can be sufficiently suppressed, the metal ion adsorbent according to the present embodiment can be used favorably as an adsorbent for removing radioactive nuclides.
  • the metal ion adsorbent according to the present embodiment is excellent for an adsorbing ability targeting strontium ions, and can be used favorably as a strontium adsorbent.
  • the metal ion adsorbent according to the present embodiment is not necessarily limited to being used and filled in an adsorption tower, and can be used as an adsorbent for all kinds of publicly known uses. Moreover, the kinds of metal to be adsorbed are not limited to radioactive nuclides, and the metal ion adsorbent can be used for adsorbing all kinds of metals.
  • the metal ion adsorbent may contain the sintered product, and may contain components in addition to the sintered product.
  • the metal ion adsorbent may be a mixture of the sintered product and other materials publicly known as adsorbents (zeolite, phosphate, antimonic acid, chelate resin, and the like).
  • the method for removing metal ions includes a step in which a treatment solution containing metal ions is brought into contact with the abovementioned metal ion adsorbent and at least a portion of the metal ions is removed from the treatment solution (hereinafter referred to in some cases as "removing step").
  • the removing step can be performed, for example, by passing the treatment solution into an adsorption tower filled with the metal ion adsorbent and bringing the treatment solution into contact with the metal ion adsorbent.
  • the removing method according to the present embodiment may include steps in addition to the abovementioned removing step.
  • the removing method may include a pretreatment step for removing a portion of the metal ions from the treatment solution before the removing step.
  • the treatment solution can be flushed through the adsorption tower at a spatial velocity of from 10 to 200 (1/hr).
  • the spatial velocity indicates a value obtained by dividing the volume of treatment solution per one hour passed through the adsorption tower by the volume of the adsorbent inside the adsorption tower.
  • Examples of pretreatment steps include an iron co-precipitation treatment step in which a portion of the metal ions in the treatment solution is removed by iron co- precipitation treatment, and a carbonate co-precipitation treatment step in which a portion of the metal ions in the treatment solution is removed by carbonate co-precipitation treatment.
  • the removing method may include one step as a pretreatment step, or may include two or more steps.
  • the removing method may include a post-treatment step for further removing metal ions from the treatment solution that has passed through the removing step.
  • a post-treatment step is a step in which the treatment solution is flushed through a column-type tower filled with a filler.
  • the removing method may include one step as a post-treatment step, or may include two or more steps.
  • the method for removing metal ions uses the metal ion adsorbent, it is ideal as a method for removing at least a portion of radioactive nuclides from a treatment solution containing radioactive nuclides, and is even more ideal as a method for removing at least a portion of strontium ions from a treatment solution containing strontium ions.
  • FIG. 1 is a schematic illustration of one embodiment of the metal ion removing equipment according to the present invention.
  • the metal ion removing equipment 100 includes iron co-precipitation treatment equipment 10, carbonate co-precipitation treatment equipment 20, a multistage adsorption tower 30, and a column-type multistage filled tower 40.
  • a treatment solution containing metal ions (for example, effluent containing radioactive nuclides) is supplied to the iron co-precipitation treatment equipment 10.
  • metal ions for example, effluent containing radioactive nuclides
  • a portion of the metal ions in the treatment solution is removed as sludge by iron co-precipitation treatment.
  • the sludge extracted from the iron co-precipitation treatment equipment 10 is stored in a storage container 1 1.
  • the treatment solution having undergone iron co-precipitation treatment is supplied to the carbonate co-precipitation treatment equipment 20.
  • the carbonate co- precipitation treatment equipment 20 a portion of the metal ions in the treatment solution is removed as sludge by carbonate co-precipitation treatment.
  • the sludge extracted from the carbonate co-precipitation treatment equipment 20 is stored in a storage container 21.
  • the treatment solution having undergone carbonate co-precipitation treatment is supplied to the multistage adsorption tower 30.
  • the multistage adsorption tower 30 has connected a plurality of adsorption towers 31 that are filled with metal ion adsorbent.
  • the multistage adsorption tower 30 has a structure in which eight adsorption towers 31 are connected in a direct series.
  • the number of adsorption towers in the multistage adsorption tower is not particularly limited.
  • the treatment solution is brought into contact with the metal ion adsorbent in the adsorption tower 31 , and the metal ions in the treatment solution are adsorbed to the metal ion adsorbent.
  • the metal ion adsorbent can be suitably exchanged in accordance with the metal ion adsorption capacity, concentration of metal ions in the treatment solution, and volume of treatment solution flushed.
  • the treatment solution passed through the multistage adsorption tower 30 is supplied to the column-type multistage filled tower 40.
  • the column-type multistage filled tower 40 has connected a plurality of column- type filled towers 41.
  • the column-type multistage filled tower 40 has a structure in which two column- type filled towers 41 are connected.
  • the column- type multistage filled tower may have a structure in which three or more column-type filled towers are connected.
  • the column-type multistage filled tower 40 the remaining metal ions are removed from the treatment solution. Moreover, the column-type multistage filled tower 40 can also function as a trap in the case in which a fine powder, or the like, of metal ion adsorbent has leaked out from the multistage adsorption tower 30.
  • the treatment solution having passed through the column- type multistage filled tower 41 is collected in a storage container 50.
  • the adsorption towers 31 filled with the above-described metal ion adsorbent are provided in the multistage adsorption tower 30. Therefore, with the metal ion removing equipment 100, excellent metal ion removing performance is exhibited, and leakage of fine powder of adsorbent from the multistage adsorption tower 30 can be sufficiently prevented.
  • the metal ion removing equipment 100 has adsorption towers 31 that are filled with the metal ion adsorbent, it is ideal as radioactive nuclide removing equipment for treating a treatment solution containing radioactive nuclides, and is also ideal as strontium removing equipment for treating a treatment solution containing strontium ions.
  • titanium tetrachloride aqueous solution (TC-36, 36% by mass titanium tetrachloride aqueous solution, manufactured by Ishihara Sangyo Kaisha) and 114 g of 1 N sodium hydroxide aqueous solution were mixed, and the eluted precipitate was collected by filtration. The precipitate was washed with water and sodium chloride produced as a byproduct was removed, whereby white solid hydrous titanium oxide was obtained.
  • the obtained hydrous titanium oxide was dispersed in water to prepare a slurry, and 2.0 g of sodium nitrate (a quantity such that the molar ratio Ci/C 2 of a content d of titanium element to a content C 2 of sodium element in the mixture was 1.21) was added to the slurry.
  • the slurry was next heated to 80°C and dried, the obtained solid was sintered for 5 hours at 400°C, and a white aggregate (sintered product) was obtained.
  • the maximum diameters in a fixed direction of any 100 particles are measured using an image obtained by SEM observation, the arithmetic mean thereof is obtained, and this is taken as the mean particle size of the particles.
  • the maximum diameters in a fixed direction of any 100 pores are measured using an image obtained by SEM observation, the arithmetic mean thereof is obtained, and this is taken as the mean pore size.
  • the sintered body obtained in Working Example 1 was crushed and graded to sizes of 0.25 to 1.0 mm. This was taken as an adsorbent sample, and the strontium adsorption ability was evaluated by the method below.
  • Percent removed (%) ((content of Sr 2+ in the simulated contaminated water) - (content of Sr 2+ in the solution for measurement)) x 100 / (content of Sr 2+ in the simulated contaminated water)
  • Examples 2 to 4 of the sintered product according to the present invention were compared with that of crystalline strontium titanate.
  • titanium tetrachloride aqueous solution (TC-36, 36% by mass titanium tetrachloride aqueous solution, manufactured by Ishihara Sangyo Kaisha, Ltd.) and 1 14 g of 1 N potassium hydroxide aqueous solution were mixed, and the eluted precipitate was collected by filtration. The precipitate was washed with water and potassium chloride produced as a byproduct was removed, whereby white solid hydrous titanium oxide was obtained.
  • the obtained hydrous titanium oxide was dispersed in water to prepare a slurry, and 1.0 g of potassium nitrate (a quantity such that the molar ratio Ci/C 2 of the content Ci of titanium element to the content C 2 of potassium element in the mixture was 2.88) was added to the slurry.
  • the slurry was next heated to 80°C and dried, the obtained solid was sintered for 2 hours at 400°C, and a white aggregate (sintered product) was obtained.
  • titanium tetrachloride aqueous solution (TC-36, 36% by mass titanium tetrachloride aqueous solution, manufactured by Ishihara Sangyo Kaisha, Ltd.) and 171 g of 1 N sodium hydroxide aqueous solution were mixed, and the eluted precipitate was collected by filtration. The precipitate was washed with water and sodium chloride produced as a byproduct was removed, whereby white solid hydrous titanium oxide was obtained.
  • the obtained hydrous titanium oxide was dispersed in water to prepare a slurry, and 1.0 g of sodium nitrate (a quantity such that the molar ratio Ci/C 2 of the content Q of titanium element to the content C 2 of sodium element in the mixture was 2.42) was added to the slurry.
  • the slurry was next heated to 80°C and dried, the obtained solid was sintered for 2 hours at 400°C, and a white aggregate (sintered product) was obtained.
  • titanium tetrachloride aqueous solution (TC-36, 36% by mass titanium tetrachloride aqueous solution, manufactured by Ishihara Sangyo Kaisha) and 114 g of 1 N sodium hydroxide aqueous solution were mixed, and the eluted precipitate was collected by filtration. The precipitate was washed with water and sodium chloride produced as a byproduct was removed, whereby white solid hydrous titanium oxide was obtained.
  • the obtained hydrous titanium oxide was dispersed in water to prepare a slurry, and 0.5 g of sodium nitrate (a quantity such that the molar ratio Ci/C 2 of the content Q of titanium element to the content C 2 of sodium element in the mixture was 4.84) was added to the slurry.
  • the slurry was next heated to 80°C and dried, the obtained solid was sintered for 2 hours at 400°C, and a white aggregate (sintered product) was obtained.
  • a crystalline powder of sodium titanate (Na 2 Ti 3 0 7 ) (manufactured by Strem Chemicals Inc.) was prepared as an adsorbent in Comparative Example 1.
  • the sintered bodies obtained in the working examples were crushed and graded to sizes of 0.25 to 1.0 mm. This was taken as an adsorbent sample, and the strontium adsorption ability was evaluated by the method below.
  • Percent removed (%) ((content of Sr 2+ in the simulated contaminated water) - (content of Sr 2+ in the solution for measurement)) x 100 / (content of Sr 2+ in the simulated contaminated water) [0100]
  • the percent removed (%) was obtained in the same manner except that the agitation time was changed to 60 minutes.
  • the percent removed (%) was obtained in the same manner using the adsorbent of Comparative Example 1 instead of the adsorbent sample. The results obtained are shown in Table 2.
  • the sintered product of the present invention has excellent metal ion adsorbing ability and can sufficiently prevent the production of fine powder in use as an adsorbent, it is useful as an adsorbent, for example, for removing radioactive nuclides from effluent from nuclear reactors, nuclear fuel reprocessing plants, and the like.

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Abstract

To provide a sintered product that has excellent metal ion adsorbing ability and can sufficiently suppress production of fine powder in use as an adsorbent. A sintered product obtained by sintering a mixture containing a hydrous titanium oxide and an alkali metal compound.

Description

SINTERED PRODUCT, METAL ION ADSORBENT, METHOD FOR REMOVING METAL IONS, AND METAL ION REMOVING EQUIPMENT
BACKGROUND
[0001 ] The present invention relates to a sintered product, a metal ion adsorbent using the sintered product, a method for removing metal ions using the metal ion adsorbent, and metal ion removing equipment.
[0002] Effluent from nuclear reactors, nuclear fuel reprocessing plants, and the like, contains many kinds of radioactive nuclides, and adsorbents for removing these hitherto have been proposed.
[0003] Japanese Unexamined Patent Application Publication No. S61 -256922 Patent
Document 1 - discloses a method for immobilizing strontium, comprising: extracting a K20 component from potassium titanate K20nTi02 (where n = 2 to 4) to obtain titania hydrate Ti02-mH20 (where m = 0 to 3); adsorbing and ion exchanging strontium in an aqueous solvent using the titania hydrate to make a sorbent body of strontium SrxO-nTi02-mH20 (where x = 0.5 to 1, n = 2 to 8, and m = 2 to 8); and heating the sorbent body of strontium to 900 to 1300°C to make a mixture of strontium titanate SrTi03 and titanium dioxide.
[0004] Japanese Patent No. 2535783 Patent Document 2 - discloses a strontium ion fixative containing a hydrous complex oxide expressed by the general formula:
Ce(HP04)x-yH20 (where x is a number in a range from 1.8 to 2.1 , and y is a number in a range from 1 to 4).
[0005] Japanese Patent No. 4428541 Patent Document 3 - discloses a sodium titanate ion exchanger containing granules having a particle size of 0.1 to 2 mm, wherein a molar ratio of sodium to titanium is 0.6 or lower, a selectivity coefficient of exchange of Na to Sr is 50,000 or higher, an ion exchange capacity is 4.5 meq/g or higher, and a distribution coefficient of radioactive strontium measured in a pH 1 1, 2.0 M NaCl aqueous solution is 40,000 ml/g or higher.
[0006] Patent Document 1 : Japanese Unexamined Patent Application Publication No.
S61-256922
Patent Document 2: Japanese Patent No. 2535783
Patent Document 3: Japanese Patent No. 4428541
SUMMARY OF THE INVENTION
[0007] An adsorbent for removing radioactive nuclides is used, for example, being filled in an adsorption tower. Effluent is passed into the adsorption tower filled with the adsorbent and the effluent is brought into contact with the adsorbent, whereby radioactive nuclides in the effluent are adsorbed to the adsorbent. [0008] In the case in which an adsorbent is used on an industrial scale, it is desirable that the granules be provided in a shape suitable for use in an adsorption tower, and the granules must have adequate mechanical strength. When the mechanical strength is insufficient, the adsorbent may be crushed into fine powder during passage and the fine powder may leak out to a latter stage from the adsorption tower. Because the fine powder leaking out is radioactive waste containing adsorbed radioactive nuclides, the fine powder must be removed by filtering or other treatment, and this is linked to lowering of operating efficiency. Moreover, transport using water flow, or the like, may be performed in order to extract spent adsorbent from the adsorption tower for the purpose of removing radioactive nuclides, but if the adsorbent is brittle, it may be crushed into fine powder by the water pressure, and there is a risk that the fine powder might clog piping.
[0009] Alkali titanate compounds are known as adsorbents for the purpose of removing strontium, but considering the purpose of removal of radioactive strontium and the use on an industrial scale, it is difficult to obtain a material that has sufficient radiation resistance and can be prepared into a particulate form suitable for column filling. Only in Japanese Patent No. 4428541 is there disclosed an ion exchanger of titanate in particulate form. In this patent, titanium oxide and an alkali agent are reacted, and the reaction solution is subjected to washing, drying, and crushing to obtain granules of ion exchanger. However, because these granules are an aggregate body due to spontaneous aggregation on drying, in the case in which the granules are dispersed in water, fine powder is produced and the supernatant becomes a colloidal solution. Therefore, even when the granules are filled into a column or an adsorption tower, fine powder continues to be produced, and therefore there is a danger that the fine powder having adsorbed radioactive strontium may wash away.
Moreover, because the strength of the granules is weak, in the case in which the granules are transported using water flow in piping, a portion of the granules may be crushed by the water pressure, and as a result, the crushed granules may clog the piping.
[0010] One aspect of the present invention relates to a sintered product from sintering a mixture containing a hydrous titanium oxide and an alkali metal compound.
[001 1 ] The sintered product has excellent metal ion adsorbing ability, and also has sufficient mechanical strength, and the production of fine powder is sufficiently suppressed in the use as an adsorbent. The reason why such effect is produced is thought to be that the alkali metal compound acts as a binding agent during sintering and improves the mechanical strength of the sintered product.
[0012] In one embodiment, the alkali metal compound may include an alkali metal nitrate. Moreover, when the alkali metal compound includes an alkali metal nitrate, the pore density of the sintered product is improved, and the metal ion adsorbing ability of the sintered product is further improved. The reason why such effect is produced is thought to be that a gas produced as a product of degradation of nitrate ions produces pores in the sintered product during sintering.
[0013] In one embodiment, a molar ratio Ci/C2 of a content d of titanium element to a content C2 of alkali metal element in the mixture is preferably from 0.5 to 5.0. When the molar ratio Ci/C2 is in this range, a sintered product having even more excellent metal ion adsorbing ability is obtained.
[0014] In one embodiment, the sintered product is preferably obtained by sintering the mixture at 100°C or higher, and preferably at from 200 to 600°C or higher. When the sintering temperature is less than 100°C, the binding effect of the alkali metal compound may not be obtained sufficiently; when the sintering temperature exceeds 600°C, a portion of the sintered product may crystallize and the metal ion adsorbing ability may be degraded. That is, by setting the sintering temperature to within the abovementioned range, the effect of the alkali metal compound as a binding agent can be obtained more effectively while suppressing crystallization of the sintered product, and both the metal ion adsorbing ability and the mechanical strength can be further improved.
[0015] In one embodiment, the sintered product is preferably porous, and a mean pore size is preferably from 0.1 to 10 μηι. Such sintered product becomes even more excellent in metal ion adsorbing ability.
[0016] In one embodiment, the sintered product may be composed of an aggregate of particles including an alkali titanate compound (hereinafter referred to in some cases as "alkali titanate particles") expressed by A2Tin02n+i (wherein A denotes an alkali metal, and n denotes from 0.5 to 5.0).
[0017] The sintered product from sintering a mixture containing a hydrous titanium oxide and an alkali metal compound can be obtained as an aggregate of alkali titanate particles. Note that although there may be cases in which aggregate forms of inorganic particles are obtained even with conventional adsorbents, it was conventionally difficult to suppress the production of fine powder due to dispersing of the inorganic particles. In contrast, with the sintered product of the present embodiment, the cohesive strength between particles is strong, and the production of fine powder is sufficiently suppressed even in the case in which the sintered product is used as an adsorbent.
[0018] In one embodiment, a mean particle size of the alkali titanate particles is preferably from 0.1 to 10 μηι. When the mean particle size is within the abovementioned range, the metal ion adsorbing ability of the sintered product is further improved.
[0019] Another aspect of the present invention relates to a metal ion adsorbent containing the above-described sintered product.
[0020] Because the metal ion adsorbent contains the above-described sintered product, it has excellent metal ion adsorbing ability. Moreover, according to this metal ion adsorbent, because leakage of fine powder to the outside of the adsorption tower is suppressed and the load of filtering or other treatment at a latter stage from the adsorption tower is reduced, improvement of operating efficiency can be achieved.
[0021 ] Moreover, another aspect of the present invention relates to a method for removing metal ions, including a step in which a treatment solution containing metal ions is brought into contact with the metal ion adsorbent and at least a portion of the metal ions is removed from the treatment solution.
[0022] Furthermore, another aspect of the present invention relates to metal ion removing equipment, including a filled tower filled with the metal ion adsorbent.
[0023] According to the present invention, a sintered product can be provided that has excellent metal ion adsorbing ability and can sufficiently suppress production of fine powder in use as an adsorbent, as well as a metal ion adsorbent containing that sintered product. Moreover, according to the present invention, a method can be provided for removing metal ions using the metal ion adsorbent, as well as metal ion removing equipment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a schematic illustration of one embodiment of the metal ion removing equipment according to the present invention.
FIG. 2 is an illustration of results of SEM observation of the sintered product of Working Example 1.
FIG. 3 is an illustration of results of SEM observation of the sintered product of Working Example 2.
DETAILED DESCRIPTION
[0025] Preferred embodiments of the present invention are described below in detail while referring to the drawings, but the present invention is not restricted to the following embodiments.
[0026] Sintered Product
The sintered product according to the present embodiment is a sintered product from sintering a mixture containing a hydrous titanium oxide and an alkali metal compound, and has excellent metal ion adsorbing ability. Moreover, the sintered product has sufficient mechanical strength, and can sufficiently suppress production of fine powder in use as an adsorbent. The reason why such effect is produced is thought to be that the alkali metal compound acts as a binding agent during sintering and improves the mechanical strength of the sintered product.
[0027] Sintering is a phenomenon in which, in general, an aggregate of solid powder is hardened by being heated to a melting temperature or lower, or to a temperature at which a partial liquid phase occurs, and a so-called "sintered body," which is a dense solid having great strength, is produced. The driving force of sintering is a force that acts to minimize the surface energy in a system composed of a particle aggregate; by application of the energy, material movement is caused between particles by solid diffusion or melting, and cohesion is brought about.
[0028] The sintered product according to the present embodiment is sintered by dissolution or solid diffusion of the alkali metal compound in the abovementioned mixture. Moreover, in the sintered product according to the present embodiment, it is thought that the alkali metal moves into the hydrous titanium oxide and an alkali titanate compound is produced. Moreover, in the case in which the alkali metal compound is an alkali metal nitrate, nitric acid gas is furthermore produced by thermolysis of the nitrate, and the sintered product becomes porous.
[0029] The hydrous titanium oxide is a compound expressed by Ti02-nH20, and can also be referred to as a "hydrate of titanium dioxide." The method for obtaining the hydrous titanium oxide is not particularly limited; for example, it can be obtained by hydrolysis of titanium tetrachloride.
[0030] Examples of alkali metals include lithium, sodium, potassium, rubidium, and cesium, and among these, lithium, sodium, and potassium are preferred.
[0031 ] Examples of alkali metal compounds include alkali metal hydroxides and alkali metal salts, and examples of alkali metal salts include alkali metal nitrates.
[0032] Moreover, a preferred alkali metal compound is one having a melting point in a range of 200 to 600°C. Such alkali metal compound melts at an optimal sintering temperature to be described, and the effect as an adsorbent can be produced effectively. For example, the melting point of sodium nitrate is 306°C, the melting point of potassium nitrate is 339°C, the melting point of sodium hydroxide is 328°C, and the melting point of potassium hydroxide is 360°C, and these alkali metal compounds can be used favorably.
[0033] The alkali metal compound more preferably includes an alkali metal nitrate.
When the alkali metal compound includes an alkali metal nitrate, the pore density of the sintered product increases, and the metal ion adsorbing ability of the sintered product tends to be further improved. The reason why such effect is produced is thought to be that pores are produced in the sintered product by a gas produced as a product of degradation of nitrate ions.
[0034] The mixture ratio of the hydrous titanium oxide and the alkali metal compound is preferably adjusted so that, for example, a molar ratio Ci/C2 of a content Q of titanium element to a content C2 of alkali metal element becomes from 0.5 to 5.0.
[0035] In the present embodiment, the sintered product is composed of an aggregate of particles including an alkali titanate compound (hereinafter referred to in some cases as
"alkali titanate particles") expressed by A2Tin02n+i (wherein A denotes an alkali metal, and n denotes from 0.5 to 5.0). [0036] The n of the alkali titanate compound can be adjusted by changing the above- described molar ratio Ci/C2. Moreover, the A originates in the alkali metal compound, and the alkali metal denoted by A may be a single kind or a plurality of kinds.
[0037] Note that although there may be cases in which aggregate forms of inorganic particles are obtained even with conventional adsorbents, it was conventionally difficult to suppress the production of fine powder due to dispersing of the inorganic particles. In contrast, in the present embodiment, the cohesive strength between particles in the aggregate is strong, and the production of fine powder is sufficiently suppressed even in the case in which the sintered product is used as an adsorbent.
[0038] A mean particle size of the alkali titanate particles is preferably from 0.1 to
10 μηι, and more preferably from 0.5 to 5 μηι. When the mean particle size of the alkali titanate particles is in the abovementioned range, the metal ion adsorbing ability of the sintered product tends to be further improved.
[0039] In the present specification, the mean particle size of the alkali titanate particles is measured by the following method. The maximum diameters in a fixed direction of any 100 alkali titanate particles are measured using an image obtained by surface observation by scanning electron microscope (hereinafter referred to in some cases as "SEM observation"), and the arithmetic mean thereof is taken as the mean particle size of the alkali titanate particles.
[0040] In the present embodiment, the sintered product is porous, and a mean pore size is preferably from 0.5 to 5 μηι. Such sintered product is even more excellent in metal ion adsorbing ability. The pores of the sintered product are not necessarily in the form of closed cells such that the mean pore size can be measured; for example, the sintered product may be porous in a form having a large number of minute gaps between alkali titanate particles (open cells).
[0041 ] In the present specification, the mean pore size of the sintered product is measured by the following method. The maximum diameters in a fixed direction of any 100 pores is measured using an image obtained by SEM observation of the sintered product, and the arithmetic mean thereof is taken as the mean pore size.
[0042] From results of X-ray diffraction, the form of primary particles constituting the alkali titanate particles is thought to be any of amorphous particles, nano-size crystalline particles, or semicrystal with mixed nano-size crystalline particles and amorphous particles.
[0043] The sintered product can be prepared, for example, by the following method.
[0044] First, an alkali metal compound is added to a slurry of hydrous titanium oxide suspended in a solvent (for example, water). Next, the solvent is removed from the slurry by drying and the solid portion is obtained, which is a mixture of hydrous titanium oxide and alkali metal compound. The sintered product is obtained by sintering the solid portion at from 200 to 600°C. [0045] The solid portion, which is a mixture of hydrous titanium oxide and alkali metal compound, aggregates by compression bonding during removal of the solvent by drying. In the present embodiment, the aggregated solid portion may be supplied as such to sintering, or may be supplied to sintering after compression molding.
[0046] Removal of the solvent by drying can be performed, for example, by heating to a temperature of 60 to 95°C. Moreover, removal of the solvent by drying can be performed under normal pressure or can be performed under reduced pressure.
[0047] The sintering time is not particularly limited, but, for example, can be from 1 to 10 hours.
[0048] The mean particle size of the alkali titanate particles can be adjusted by changing the particle size of the hydrous titanium oxide in the slurry. For example, alkali titanate particles having a small mean particle size can be obtained by reducing the particle size of the hydrous titanium oxide in the slurry.
[0049] The sintered product may be used as such as a metal ion adsorbent, or may be used upon crushing to a size adapted for the use. For example, in use as an adsorbent to be filled in an adsorption tower, the sintered product is preferably used in granular form, and the particle size of the granules is preferably from 0.01 to 5 mm, and more preferably from 0.2 to 2 mm.
[0050] Metal Ion Adsorbent
The metal ion adsorbent according to the present embodiment contains the sintered product. Because the metal ion adsorbent according to the present embodiment contains the sintered product, it has excellent metal ion adsorbing ability.
[0051 ] Moreover, according to this metal ion adsorbent, because leakage of fine powder to the outside of the adsorption tower is sufficiently suppressed and the load of filtering or other treatment at a latter stage from the adsorption tower is reduced, improvement of operating efficiency can be achieved.
[0052] Particularly in the case in which the adsorbent is used for removing radioactive nuclides (for example, cesium, strontium, or the like) from effluent in nuclear reactors, nuclear fuel reprocessing plants, and the like, because the leakage of fine powder is leakage of radioactive waste, the treatment thereof involves an excessive operating load and a corresponding danger. According to the metal ion adsorbent according to the present embodiment, because this leakage of fine powder can be sufficiently suppressed, the metal ion adsorbent according to the present embodiment can be used favorably as an adsorbent for removing radioactive nuclides.
[0053] Moreover, because spent adsorbent may be transported using water flow in use for removal of radioactive nuclides, if the adsorbent is brittle and is easily crushed into fine powder, there is a risk that the fine powder might clog piping. On this point, according to the metal ion adsorbent according to the present embodiment, because the production of fine powder is sufficiently suppressed, the occurrence of clogging of piping during transport by water flow can be prevented.
[0054] Moreover, although cesium, among radioactive nuclides, can be removed comparatively easily by co-precipitation, or the like, a method for removing strontium from the effluent has not been fully established. The metal ion adsorbent according to the present embodiment is excellent for an adsorbing ability targeting strontium ions, and can be used favorably as a strontium adsorbent.
[0055] The metal ion adsorbent according to the present embodiment is not necessarily limited to being used and filled in an adsorption tower, and can be used as an adsorbent for all kinds of publicly known uses. Moreover, the kinds of metal to be adsorbed are not limited to radioactive nuclides, and the metal ion adsorbent can be used for adsorbing all kinds of metals.
[0056] The metal ion adsorbent may contain the sintered product, and may contain components in addition to the sintered product. For example, the metal ion adsorbent may be a mixture of the sintered product and other materials publicly known as adsorbents (zeolite, phosphate, antimonic acid, chelate resin, and the like).
[0057] Method for Removing Metal Ions
The method for removing metal ions according to the present embodiment includes a step in which a treatment solution containing metal ions is brought into contact with the abovementioned metal ion adsorbent and at least a portion of the metal ions is removed from the treatment solution (hereinafter referred to in some cases as "removing step").
[0058] The removing step can be performed, for example, by passing the treatment solution into an adsorption tower filled with the metal ion adsorbent and bringing the treatment solution into contact with the metal ion adsorbent.
[0059] The removing method according to the present embodiment may include steps in addition to the abovementioned removing step. For example, the removing method may include a pretreatment step for removing a portion of the metal ions from the treatment solution before the removing step.
[0060] In the removing step, for example, the treatment solution can be flushed through the adsorption tower at a spatial velocity of from 10 to 200 (1/hr). The spatial velocity indicates a value obtained by dividing the volume of treatment solution per one hour passed through the adsorption tower by the volume of the adsorbent inside the adsorption tower.
[0061 ] Examples of pretreatment steps include an iron co-precipitation treatment step in which a portion of the metal ions in the treatment solution is removed by iron co- precipitation treatment, and a carbonate co-precipitation treatment step in which a portion of the metal ions in the treatment solution is removed by carbonate co-precipitation treatment. The removing method may include one step as a pretreatment step, or may include two or more steps.
[0062] Moreover, the removing method may include a post-treatment step for further removing metal ions from the treatment solution that has passed through the removing step. An example of a post-treatment step is a step in which the treatment solution is flushed through a column-type tower filled with a filler. The removing method may include one step as a post-treatment step, or may include two or more steps.
[0063] Because the method for removing metal ions according to the present embodiment uses the metal ion adsorbent, it is ideal as a method for removing at least a portion of radioactive nuclides from a treatment solution containing radioactive nuclides, and is even more ideal as a method for removing at least a portion of strontium ions from a treatment solution containing strontium ions.
[0064] Metal Ion Removing Equipment
FIG. 1 is a schematic illustration of one embodiment of the metal ion removing equipment according to the present invention. The metal ion removing equipment 100 includes iron co-precipitation treatment equipment 10, carbonate co-precipitation treatment equipment 20, a multistage adsorption tower 30, and a column-type multistage filled tower 40.
[0065] A treatment solution containing metal ions (for example, effluent containing radioactive nuclides) is supplied to the iron co-precipitation treatment equipment 10. In the iron co-precipitation treatment equipment 10, a portion of the metal ions in the treatment solution is removed as sludge by iron co-precipitation treatment. The sludge extracted from the iron co-precipitation treatment equipment 10 is stored in a storage container 1 1.
[0066] The treatment solution having undergone iron co-precipitation treatment is supplied to the carbonate co-precipitation treatment equipment 20. In the carbonate co- precipitation treatment equipment 20, a portion of the metal ions in the treatment solution is removed as sludge by carbonate co-precipitation treatment. The sludge extracted from the carbonate co-precipitation treatment equipment 20 is stored in a storage container 21.
[0067] The treatment solution having undergone carbonate co-precipitation treatment is supplied to the multistage adsorption tower 30. The multistage adsorption tower 30 has connected a plurality of adsorption towers 31 that are filled with metal ion adsorbent. In the metal ion removing equipment 100, the multistage adsorption tower 30 has a structure in which eight adsorption towers 31 are connected in a direct series. However, in the equipment for removing metal ions of the present embodiment, the number of adsorption towers in the multistage adsorption tower is not particularly limited.
[0068] In the multistage adsorption tower 30, the treatment solution is brought into contact with the metal ion adsorbent in the adsorption tower 31 , and the metal ions in the treatment solution are adsorbed to the metal ion adsorbent. The metal ion adsorbent can be suitably exchanged in accordance with the metal ion adsorption capacity, concentration of metal ions in the treatment solution, and volume of treatment solution flushed.
[0069] The treatment solution passed through the multistage adsorption tower 30 is supplied to the column-type multistage filled tower 40. The column-type multistage filled tower 40 has connected a plurality of column- type filled towers 41. In the metal ion removing equipment 100, the column-type multistage filled tower 40 has a structure in which two column- type filled towers 41 are connected. However, the column- type multistage filled tower may have a structure in which three or more column-type filled towers are connected.
[0070] In the column-type multistage filled tower 40, the remaining metal ions are removed from the treatment solution. Moreover, the column-type multistage filled tower 40 can also function as a trap in the case in which a fine powder, or the like, of metal ion adsorbent has leaked out from the multistage adsorption tower 30.
[0071 ] The treatment solution having passed through the column- type multistage filled tower 41 is collected in a storage container 50.
[0072] In the metal ion removing equipment 100, the adsorption towers 31 filled with the above-described metal ion adsorbent are provided in the multistage adsorption tower 30. Therefore, with the metal ion removing equipment 100, excellent metal ion removing performance is exhibited, and leakage of fine powder of adsorbent from the multistage adsorption tower 30 can be sufficiently prevented.
[0073] Moreover, because the metal ion removing equipment 100 has adsorption towers 31 that are filled with the metal ion adsorbent, it is ideal as radioactive nuclide removing equipment for treating a treatment solution containing radioactive nuclides, and is also ideal as strontium removing equipment for treating a treatment solution containing strontium ions.
[0074] A preferred embodiment of the present invention was described above, but the present invention is not limited to the abovementioned embodiment.
Examples
[0075] The present invention is described more specifically below using working examples, but the present invention is not limited to the working examples.
[0076] Working Example 1
15 g of titanium tetrachloride aqueous solution (TC-36, 36% by mass titanium tetrachloride aqueous solution, manufactured by Ishihara Sangyo Kaisha) and 114 g of 1 N sodium hydroxide aqueous solution were mixed, and the eluted precipitate was collected by filtration. The precipitate was washed with water and sodium chloride produced as a byproduct was removed, whereby white solid hydrous titanium oxide was obtained.
[0077] The obtained hydrous titanium oxide was dispersed in water to prepare a slurry, and 2.0 g of sodium nitrate (a quantity such that the molar ratio Ci/C2 of a content d of titanium element to a content C2 of sodium element in the mixture was 1.21) was added to the slurry. The slurry was next heated to 80°C and dried, the obtained solid was sintered for 5 hours at 400°C, and a white aggregate (sintered product) was obtained.
[0078] Surface observation of the sintered product obtained in Working Example 1 was performed by scanning electron microscope (hereinafter referred to as "SEM."). The results of observation are shown in FIG. 2. It was confirmed from the results of SEM observation that the sintered product was an aggregate of particles and was porous. Moreover, a mean particle size calculated by the method below from the results of SEM observation was 1.6 μηι. Moreover, a mean pore size calculated by the method below from the results of SEM observation was 2.1 μηι.
[0079] Calculation of mean particle size:
The maximum diameters in a fixed direction of any 100 particles are measured using an image obtained by SEM observation, the arithmetic mean thereof is obtained, and this is taken as the mean particle size of the particles.
[0080] Calculation of mean pore size:
The maximum diameters in a fixed direction of any 100 pores are measured using an image obtained by SEM observation, the arithmetic mean thereof is obtained, and this is taken as the mean pore size.
[0081] Evaluation of adsorbent:
The sintered body obtained in Working Example 1 was crushed and graded to sizes of 0.25 to 1.0 mm. This was taken as an adsorbent sample, and the strontium adsorption ability was evaluated by the method below.
[0082] 1.5 g of the adsorbent sample and 150 ml of simulated contaminated water
(NaCl content: 10000 ppm, Ca2+ content: 16 ppm, Mg2+ content: 10 ppm, Sr2+ content: 10 ppm) were put into a 200 ml sealed container, and the contents were agitated by vibrating machine at conditions of 1 10 rpm, 3.7 cm vibration amplitude, and 0.5 hours. After agitation, centrifuging (3000 rpm, 5 minutes) was performed, and the supernatant was then filtered using a 0.45 μηι filter to obtain a liquid for measurement.
[0083] ICP optical emission spectroscopy of the obtained solution for measurement was performed, the content of Sr2+ in the solution for measurement was quantified and the percent removed (%) was obtained by the following formula.
Percent removed (%) = ((content of Sr2+ in the simulated contaminated water) - (content of Sr2+ in the solution for measurement)) x 100 / (content of Sr2+ in the simulated contaminated water)
[0084] Next, the percent removed (%) in cases in which the agitation time was changed to 1.0 hours, 2.0 hours, 4.0 hours, and 24 hours was measured by the same method. The results obtained are shown in Table 1. Note that ">99.9" in Table 1 indicates a result at or above the measurement limit (content of Sr2+ in the solution for measurement is at or below the measurement limit). [0085] Moreover, during the analysis, the visual appearance of the supernatant after sitting still for one minute after agitation was observed. The extent of production of fine powder of adsorbent was evaluated as A in the case in which the supernatant was transparent and as B in the case in which the supernatant was clouded white with fine powder. The evaluation results are shown in Table 1. Note that the samples evaluated as B in the working examples were not observed.
[0086] Table 1
[0087] Next, the strontium adsorbing abilities of a plurality of modes (Working
Examples 2 to 4) of the sintered product according to the present invention were compared with that of crystalline strontium titanate.
[0088] Working Example 2
15 g of titanium tetrachloride aqueous solution (TC-36, 36% by mass titanium tetrachloride aqueous solution, manufactured by Ishihara Sangyo Kaisha, Ltd.) and 1 14 g of 1 N potassium hydroxide aqueous solution were mixed, and the eluted precipitate was collected by filtration. The precipitate was washed with water and potassium chloride produced as a byproduct was removed, whereby white solid hydrous titanium oxide was obtained.
[0089] The obtained hydrous titanium oxide was dispersed in water to prepare a slurry, and 1.0 g of potassium nitrate (a quantity such that the molar ratio Ci/C2 of the content Ci of titanium element to the content C2 of potassium element in the mixture was 2.88) was added to the slurry. The slurry was next heated to 80°C and dried, the obtained solid was sintered for 2 hours at 400°C, and a white aggregate (sintered product) was obtained.
[0090] Surface observation of the sintered product obtained in working example 2 was performed by SEM. The results of observation are shown in FIG. 3. It was confirmed from the results of SEM observation that the sintered product was an aggregate of particles and was porous. Moreover, the mean particle size calculated by the above method from the results of SEM observation was 0.81 μηι. Although a large number of pores was observed between aggregated particles in the sintered product obtained in working example 2, the mean pore size could not be calculated because the pores were not in the form of closed cells.
[0091] Working Example 3
15 g of titanium tetrachloride aqueous solution (TC-36, 36% by mass titanium tetrachloride aqueous solution, manufactured by Ishihara Sangyo Kaisha, Ltd.) and 171 g of 1 N sodium hydroxide aqueous solution were mixed, and the eluted precipitate was collected by filtration. The precipitate was washed with water and sodium chloride produced as a byproduct was removed, whereby white solid hydrous titanium oxide was obtained.
[0092] The obtained hydrous titanium oxide was dispersed in water to prepare a slurry, and 1.0 g of sodium nitrate (a quantity such that the molar ratio Ci/C2 of the content Q of titanium element to the content C2 of sodium element in the mixture was 2.42) was added to the slurry. The slurry was next heated to 80°C and dried, the obtained solid was sintered for 2 hours at 400°C, and a white aggregate (sintered product) was obtained.
[0093] Surface observation of the sintered product obtained in Working Example 3 was performed by SEM. It was confirmed from the results of SEM observation that the sintered product was an aggregate of particles and was porous. Moreover, the mean particle size calculated by the above method from the results of SEM observation was 0.81 μηι.
Moreover, the mean pore size calculated by the above method from the results of SEM observation was 0.92 μηι.
[0094] Working Example 4
15 g of titanium tetrachloride aqueous solution (TC-36, 36% by mass titanium tetrachloride aqueous solution, manufactured by Ishihara Sangyo Kaisha) and 114 g of 1 N sodium hydroxide aqueous solution were mixed, and the eluted precipitate was collected by filtration. The precipitate was washed with water and sodium chloride produced as a byproduct was removed, whereby white solid hydrous titanium oxide was obtained.
[0095] The obtained hydrous titanium oxide was dispersed in water to prepare a slurry, and 0.5 g of sodium nitrate (a quantity such that the molar ratio Ci/C2 of the content Q of titanium element to the content C2 of sodium element in the mixture was 4.84) was added to the slurry. The slurry was next heated to 80°C and dried, the obtained solid was sintered for 2 hours at 400°C, and a white aggregate (sintered product) was obtained.
[0096] Comparative Example 1
A crystalline powder of sodium titanate (Na2Ti307) (manufactured by Strem Chemicals Inc.) was prepared as an adsorbent in Comparative Example 1.
[0097] Evaluation of strontium adsorbing ability:
The sintered bodies obtained in the working examples were crushed and graded to sizes of 0.25 to 1.0 mm. This was taken as an adsorbent sample, and the strontium adsorption ability was evaluated by the method below.
[0098] 1.0 g of the adsorbent sample and 300 ml of simulated contaminated water
(NaCl content: 10000 ppm, Ca2+ content: 16 ppm, Mg2+ content: 10 ppm, Sr2+ content: 10 ppm) were put into a beaker, and the contents were agitated by stirrer for 30 minutes. After agitation, centrifuging (3000 rpm, 5 minutes) was performed, and the supernatant was filtered using a 0.45 μηι filter to obtain a liquid for measurement.
[0099] ICP optical emission spectroscopy of the obtained solution for measurement was performed, the content (ppm) of Sr2+ in the solution for measurement was quantified, and the percent removed (%) was obtained by the following formula.
Percent removed (%) = ((content of Sr2+ in the simulated contaminated water) - (content of Sr2+ in the solution for measurement)) x 100 / (content of Sr2+ in the simulated contaminated water) [0100] Next, the percent removed (%) was obtained in the same manner except that the agitation time was changed to 60 minutes. Furthermore, the percent removed (%) was obtained in the same manner using the adsorbent of Comparative Example 1 instead of the adsorbent sample. The results obtained are shown in Table 2.
[0101] Table 2
[0102] Because the sintered product of the present invention has excellent metal ion adsorbing ability and can sufficiently prevent the production of fine powder in use as an adsorbent, it is useful as an adsorbent, for example, for removing radioactive nuclides from effluent from nuclear reactors, nuclear fuel reprocessing plants, and the like.

Claims

What is Claimed is:
1. A sintered product from sintering a mixture containing a hydrous titanium oxide and an alkali metal compound.
2. The sintered product according to claim 1 , wherein the alkali metal compound includes an alkali metal nitrate.
3. The sintered product according to claim 1 or 2, wherein a molar ratio Ci/C2 of a content d of titanium element to a content C2 of alkali metal element in the mixture is from 0.5 to 5.0.
4. The sintered product according to any one of claims 1 to 3, wherein the mixture is sintered at from 200 to 600°C.
5. The sintered product according to any one of claims 1 to 4, wherein the sintered product is porous, and a mean pore size is from 0.1 to 10 μιη.
6. The sintered product according to any one of claims 1 to 5, wherein the sintered product is composed of an aggregate of particles including an alkali titanate compound expressed by A2Tin02n+i (wherein A denotes an alkali metal, and n denotes from 0.5 to 5.0).
7. The sintered product according to any one of claims 1 to 6, wherein a mean particle size of the particles is from 0.1 to 10 μιη.
8. A metal ion adsorbent, containing the sintered product according to any one of claims 1 to 7.
9. A method for removing metal ions, comprising a step in which a treatment solution containing metal ions is brought into contact with the metal ion adsorbent according to claim 8 and at least a portion of the metal ions is removed from the treatment solution.
10. Metal ion removing equipment, comprising a filled tower filled with the metal ion adsorbent according to claim 8.
PCT/US2013/041341 2012-05-22 2013-05-16 Sintered product, metal ion adsorbent, method for removing metal ions, and metal ion removing equipment WO2013176956A2 (en)

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