JP2015042395A - Method for producing strontium adsorbent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a strontium adsorbent, in which the strontium adsorbent, whose mechanical strength is enhanced sufficiently without damaging alkali metal titanate-intrinsic adsorptive performance, is produced by mixing clay being aggregate and a high-molecular alcohol aqueous solution being a plasticizer in alkali metal titanate powder by predetermined ratios to obtain a mixture, granulating the mixture to obtain a granulated material, and firing the granulated material.SOLUTION: The method for producing the strontium adsorbent comprises: a mixing step of mixing clay, high-molecular alcohol and water in the alkali metal titanate powder; a granulation step of granulating the obtained mixture; and a firing step of firing the obtained granulated material under an oxygen-containing atmosphere. At the firing step, preliminary firing of 200-300°C and normal firing of 650-850°C are performed.

Description

  The present invention relates to a method for producing a strontium adsorbent, and more specifically, an alkali metal titanate powder is mixed with an aqueous polymer alcohol solution at a predetermined ratio using clay as a plasticizer as an aggregate, and granulated and fired. Thus, the present invention relates to a method for producing a strontium adsorbent with sufficiently increased mechanical strength without impairing the original adsorption performance of the alkali metal titanate. The present invention also relates to a strontium adsorbent produced by the method for producing a strontium adsorbent, and an adsorption vessel, an adsorption tower and a water treatment apparatus using the strontium adsorbent.

Like radioactive cesium, radioactive strontium ⁹⁰ Sr is a fission product having a long half-life, easily dissolved in water, and highly diffusible in water. Like radioactive cesium, water contaminated by radioactive strontium In addition, the development of purification technology has become an issue. In particular, the development of an adsorbent capable of selectively adsorbing and removing radioactive strontium from radioactive wastewater with a high salt concentration such as seawater mixed therein is desired.

⁹⁰ Sr undergoes β decay and changes to stable ⁹⁰ Zr via ⁹⁰ Y, but at that time, a large decay heat is generated. Therefore, when the used adsorbent treated with radioactive wastewater containing ⁹⁰ Sr at a high dose is stored for a long period of time, after the adhering water evaporates, the temperature inside the adsorbent packed bed rises due to decay heat and becomes high. For example, when the adsorbent adsorbs 2 × 10 ¹¹ Bq / L of ⁹⁰ Sr, the calorific value reaches 20 W / m ^3, and when such a used adsorbent is stored in a container having an inner diameter of about 1.5 m, The vicinity of the center of the adsorbent packed bed is estimated to be about 15 ° C. higher than the ambient temperature. Therefore, when ⁹⁰ Sr is adsorbed by 5 × 10 ¹¹ Bq / L, the temperature difference reaches 50 ° C. . Therefore, as a radioactive strontium adsorbent, a general cation exchange resin composed of a divinylbenzenesulfonic acid-based organic material is inappropriate. In addition, a normal cation exchange resin is a radioactive wastewater contaminated with radioactive strontium in that it cannot selectively adsorb only strontium from wastewater containing a high concentration of cations such as Na ⁺ and Mg ^2+. It is not compatible with the processing.

  For this reason, it is desirable to employ an inorganic ion exchanger having high selectivity for strontium as an adsorbent for adsorbing and removing radioactive strontium from radioactive wastewater with a high salt concentration.

As a treatment technique of radioactive strontium using an inorganic material, Non-Patent Document 1 reports that radioactive strontium in water is removed by adsorption with orthotitanic acid.
Further, in Patent Document 1, as a method for producing a sodium titanate ion exchanger that adsorbs radioactive strontium, hydrous titanium oxide is slurried with a liquid composed of alcohol and sodium hydroxide, heated, filtered, dried, A method for classifying and producing granular sodium titanate having a sodium / titanium molar ratio of 0.6 or less has been proposed.

  By the way, generally, the adsorbent used in the water treatment process is usually transported as a slurry using water as a dispersion medium when the adsorption tower is filled in the treatment tower or discharged from the adsorption tower after use. Moreover, when water flow is continued for a long period of time, it is always used in a state of receiving water flow pressure. From such a viewpoint, it is desirable that the adsorbent for water treatment is in the form of particles having a particle diameter of about 150 to 3,000 μm having a mechanical strength of a certain level or more.

For example, JIS K1474 defines a strength test method for activated carbon, and the method is as follows.
(1) Add the agent to the sieve (aperture: 1.18-0.300 mm) and put it on a sieve shaker for 10 minutes.
(2) Tapping the container to the 100 mL mark of the 200 mL graduated cylinder and filling the screened sample, weigh the agent to the order of 0.1 g.
(3) Prepare 15 steel balls with diameters of 12.7 mm and 9.5 mm, respectively, put them together with the agent weighed in (2) into a sieve pan (bottom receiving tray) and shake for 30 minutes on a shaker.
(4) Using a sieve with an aperture of 0.150 mm, put a sample other than the steel ball of (3) and put it on a sieve shaker for 3 minutes.
(5) Weigh each of the sample remaining on the sieve and the sample remaining on the sieve pan (bottom tray) (W is the sample remaining on the sieve, and S is the total sample amount on the sieve and the pan).
* If S increases or decreases by 2% or more with respect to the weight of (2), start over.
(6) Calculate hardness (H) by the following formula.
H = W / S × 100

  The activated carbon used for water treatment is preferably 80% or more in hardness (hereinafter sometimes referred to as “strength index (H)”) obtained by the above method.

Granular sodium titanate produced by the method of Patent Document 1 is indefinite and does not use aggregates, so its mechanical strength increases the required strength index (H) of the activated carbon. Below.
In the treatment of radioactive wastewater, it is important to ensure stable operation. However, in such an adsorbent that has low mechanical strength and generates fine powder due to the collapse of the adsorbent, there is a risk of causing water flow obstruction due to blockage of the strainer and the like. is there. In addition, in the treatment of radioactive wastewater, in order to measure the evaluation of wastewater properties by dose, if fine powder of adsorbent that adsorbs radioactive strontium is generated and discharged in a state mixed with treated water, the dose of treated water The standard value may not be satisfied.

  Patent Document 2 discloses a method for producing a granular adsorbent having a sufficient mechanical strength without significantly deteriorating the adsorption characteristics using an alkali metal titanate that is an inorganic ion exchanger having selectivity for strontium as a base material. In addition, an alkali metal titanate powder, a clay-based aggregate, an alcohol plasticizer for imparting plasticity and water are added, kneaded, granulated, dried, and then dried in an air atmosphere. A method of firing in a heating furnace has been proposed.

Japanese Patent No. 4428541 Japanese Patent Application No. 2012-122215

Masumi Kubota et al. “Development of group separation method: Development of treatment method of waste liquid containing 90Sr and 134Cs by inorganic ion exchanger column method” JAERI-M82-144 (1982)

  If it is the technique of patent document 2, the granular adsorbent which has sufficient mechanical strength can be manufactured, without impairing an adsorption characteristic large, However, The further improvement is desired in the following points.

The alkali metal titanate used as the base material preferably has a layered crystal structure, for example, potassium dititanate, sodium trititanate, potassium tetratitanate, and the like. Is thermally unstable and, when baked at a high temperature above a certain level, the layered crystal structure collapses and the ion exchange capacity is greatly impaired.
On the other hand, the clay used as the aggregate is improved in mechanical strength as it is fired at a high temperature.
From this point of view, Patent Document 2 also describes that there is an appropriate range for the firing temperature, the particle strength is weak when the firing temperature is low, and the adsorption performance is lowered when it is high. That is, the adsorption performance and the mechanical strength are in a trade-off relationship with each other under the firing temperature condition, and based on an alkali metal titanate having sufficient mechanical strength while maintaining both ion exchange capacity. In order to produce a granular strontium adsorbent as a material, it is necessary to set more appropriate firing conditions.

  In the present invention, the alkali metal titanate powder is mixed with a clay as a plasticizer and a polymer alcohol aqueous solution in a predetermined ratio as a plasticizer, and granulated and fired to produce a strontium adsorbent. It is an object of the present invention to provide a method for producing a strontium adsorbent having a sufficiently high mechanical strength while maintaining a higher adsorption performance.

  As a result of intensive studies to solve the above problems, the present inventors have maintained the adsorption performance higher, and at the same time, the optimum temperature for producing a strontium adsorbent with sufficiently increased mechanical strength. The profile was found and the present invention was completed.

  That is, the gist of the present invention is as follows.

[1] Mixing step of mixing alkali metal titanate powder with clay, polymer alcohol and water, granulating step of granulating the obtained mixture, and the resulting granulated product in an oxygen-containing atmosphere In the manufacturing method of the strontium adsorbent which has a baking process baked in, this baking process includes the preliminary baking process baked at 200-300 degreeC, and the main baking process baked at 650-850 degreeC, It is characterized by the above-mentioned. A method for producing a strontium adsorbent.

[2] In [1], the method includes a temperature raising step for increasing the temperature from the preliminary baking temperature to the main baking temperature at a heating rate of 50 to 150 ° C./hr between the preliminary baking step and the main baking step. The preliminary calcination step is performed for 1 to 3 hours, and the main calcination step is performed for 1 to 3 hours. After the main calcination, the temperature is decreased to a temperature of 90 to 110 ° C. at a temperature decrease rate of 100 to 250 ° C./hr. A method for producing a strontium adsorbent, wherein the temperature is lowered at a temperature of ° C / hr.

[3] The method for producing a strontium adsorbent according to [1] or [2], further comprising a drying step of drying the granulated body at 80 to 180 ° C. prior to the firing step.

[4] The method for producing a strontium adsorbent according to any one of [1] to [3], wherein the firing in the firing step is performed in an electric tunnel furnace, a gas combustion tunnel furnace, or a batch-type rotary furnace. .

[5] The method for producing a strontium adsorbent according to any one of [1] to [4], wherein the oxygen concentration in the atmosphere in the firing step is 10% by volume or more.

[6] In any one of [1] to [5], the granulated body is a granule having an average particle diameter of 150 to 3000 μm, and the granulated body is disposed in a layer form having a thickness of 5 to 30 mm and fired. A method for producing a strontium adsorbent characterized by the above.

[7] In any one of [1] to [6], 5 to 30 parts by weight of clay, 2 to 10 parts by weight of a polymer alcohol, and 50 to 120 parts by weight of water with respect to 100 parts by weight of the alkali metal titanate powder. A method for producing a strontium adsorbent characterized by mixing parts.

[8] A strontium adsorbent produced by the method for producing a strontium adsorbent according to any one of [1] to [7].

[9] An adsorption container filled with the strontium adsorbent according to [8].

[10] An adsorption tower comprising the strontium adsorbent according to [8].

[11] A water treatment apparatus comprising the adsorption container according to [9] or the adsorption tower according to [10].

  According to the present invention, a strontium adsorbent having excellent adsorption performance and high mechanical strength can be produced.

It is a graph which shows the column water-flow test result in Example 7 and Comparative Example 5.

  Hereinafter, embodiments of the present invention will be described in detail. However, the embodiments described below are for facilitating the understanding of the present invention and are not intended to limit the present invention. In the range which does not exceed the gist, each element disclosed in the following embodiments can be implemented with various modifications.

  The method for producing a strontium adsorbent of the present invention was obtained by mixing a clay, a polymer alcohol, and water with an alkali metal titanate powder, and a granulation step for granulating the obtained mixture. A firing step of firing the granulated body in an oxygen-containing atmosphere, and performing a preliminary firing step of firing at 200 to 300 ° C. and a main firing step of firing at 650 to 850 ° C. in the firing step. .

  In the present invention, the polymer alcohol in the granulated body is oxidatively decomposed and removed in the preliminary firing step of firing at a low temperature of 200 to 300 ° C., and then the clay is sintered in the main firing step of 650 to 850 ° C. To obtain a strontium adsorbent with high mechanical strength. In this way, the baking process is performed in two stages, a low temperature pre-baking process for burning and removing the polymer alcohol and a high temperature main baking process for sintering the clay, so that the polymer alcohol can be obtained in the low temperature pre-baking process. During combustion, the influence of reaction heat generated by the oxidative decomposition reaction of the polymer alcohol is suppressed, and in the subsequent main firing step, firing is performed at a high temperature necessary for clay sintering, and an adsorbent with high mechanical strength. Get.

  Preferably, the method for producing a strontium adsorbent according to the present invention includes a drying step between the granulation step and the firing step, and the firing step is a primary temperature rise in which the temperature is raised from room temperature to a pre-baking temperature. A pre-baking step of baking at a predetermined pre-baking temperature, a secondary heating step of raising the temperature from the pre-baking temperature to the main baking temperature, a main baking step of baking at a predetermined main baking temperature, and a main baking temperature And a temperature lowering step for lowering the temperature from room temperature to room temperature.

[Mixing process]
In the method for producing a strontium adsorbent of the present invention, first, an alkali metal titanate powder, clay, a polymer alcohol and water are mixed to prepare a mixture.

<Alkali metal titanate>
The alkali metal titanate is a base material (adsorption component) of the strontium adsorbent, and preferably has a layered crystal structure as described above, and potassium dititanate (K ₂ Ti ₂ O ₅ ), Examples thereof include sodium trititanate (Na ₂ Ti ₃ O ₇ ) and potassium tetratitanate (K ₂ Ti ₄ O ₉ ).

  The alkali metal titanate used in the present invention is preferably in the form of a powder having an average particle diameter in the range of 1 to 150 μm. Here, the average particle diameter can be measured by, for example, a laser diffraction particle size distribution measuring apparatus.

When the average particle diameter of the alkali metal titanate is in the range of 1 to 150 μm, the adsorption capacity is high, and the handling is advantageous in the subsequent granulation step. That is, if the average particle size is 1 μm or more, there are no manufacturing difficulties such as scattering or electrostatic adhesion to the container, and if the average particle size is 150 μm or less, the adsorption capacity decreases due to a decrease in specific surface area. I don't have to.
Therefore, in the present invention, it is preferable to use an alkali metal titanate having such a particle size. The average particle diameter of the alkali metal titanate is more preferably 4 to 30 μm.

  Only 1 type may be used for alkali metal titanate, and 2 or more types may be mixed and used for it.

<Clay>
Clay functions as an aggregate (binder). For example, clay minerals such as bentonite, attapulgite, sepiolite, allophane, halloysite, imogolite, and kaolinite can be used. Among these clay minerals, it is preferable to use fibrous clay minerals such as attapulgite and sepiolite from the viewpoint of the mechanical strength of the granulated body. These may be used individually by 1 type, and may mix and use 2 or more types.

<Polymer alcohol>
The polymer alcohol functions as a plasticizer that gives plasticity necessary for granulation, and examples thereof include polyethylene glycol and polyvinyl alcohol (PVA). The higher degree of polymerization of the polymer alcohol is preferable in terms of improving the viscosity, and specifically about 500 to 2000 is preferable. These polymer alcohols may be used alone or in combination of two or more.

  In the mixing step, the polymer alcohol is preferably mixed with the alkali metal titanate powder and clay as an aqueous solution of about 2 to 20% by weight.

<Other additives>
In this invention, you may mix | blend and use additives other than the said alkali metal titanate powder, clay, and polymeric alcohol as needed for manufacture of a strontium adsorbent. As other additives, anti-sticking agents such as crystalline cellulose can be used.

<Mixing ratio>
The clay is preferably used in an amount of 5 to 30 parts by weight, particularly 10 to 25 parts by weight, based on 100 parts by weight of the alkali metal titanate powder. If the amount of clay used is too small, the strength of the adsorbent obtained tends to be insufficient, while if too large, the content of the alkali metal titanate tends to be relatively small and the adsorption performance tends to decrease.

  The polymer alcohol is preferably used in an amount of 2 to 10 parts by weight, particularly about 3 to 8 parts by weight, based on 100 parts by weight of the alkali metal titanate powder. If the amount of the polymer alcohol used is within the above range, excellent granulation moldability can be obtained.

Water is 50 to 120 parts by weight, particularly 60 to 100 parts by weight, based on 100 parts by weight of the alkali metal titanate powder, and the solid-liquid concentration other than water in the mixture is 25 to 60% by weight, particularly 35 to 50%. It is preferable to use so that it may become about weight%.
When the amount of water used is within the above range, excellent kneading properties and granulation moldability can be obtained.

  When other additives are blended, the amount of other additives added is not particularly limited as long as it does not impair the effects of the present invention, but usually 100 parts by weight of alkali metal titanate powder. And 10 parts by weight or less.

<Mixing method>
As a method of mixing alkali metal titanate powder, clay, polymer alcohol, water and other additives used as necessary, they are mixed uniformly enough by applying a large shearing force during mixing. There is no particular limitation as long as the method can be used, but mixing is preferably performed with a mixing / kneader equipped with a stirring blade in a cylindrical container or a conical container. The shape of the stirring blade is not particularly specified, but may be a paddle shape, a ribbon shape, a propeller shape, or an anchor shape, and the rotation may be a uniaxial or biaxial planet. Further, mixing and granulation can be performed using an extrusion granulator.

[Granulation process]
There is no restriction | limiting in particular as a method of granulating the mixture obtained at the said mixing process, The rolling granulation method using a drum type granulator, a dish type granulator, etc .; a flexo mix, a vertical granulator, etc. Mixing and agitation granulation method using a screw; extrusion granulation method using a screw type extrusion granulator, a roll type extrusion granulator, a blade type extrusion granulator, a self-molding type extrusion granulator, etc .; Compression granulation method using a granulator, briquette type granulator, etc .; fluidized bed granulation method, etc. are mentioned, but in consideration of forming into a granule suitable for the present invention, rolling granulation method or mixing Agitation granulation is preferred. A method of forming a columnar granule using an extrusion granulator and then forming it into a spherical shape using a molding machine such as a Malmerizer is also preferred.

The shape of the granulated body obtained by granulation is preferably spherical, but may be a columnar shape, a disk shape, or other shapes.
The size of the granulated body is 150 to 3000 μm, preferably 300 to 2000 μm, as an average particle size of the granulated body after drying described later. If the size of the granulated body is larger than the above range, the surface area becomes small, so that the strontium adsorption ability is lowered, and if it is small, there is a risk of leakage from a strainer such as an adsorption tower.
Here, the particle diameter of the granulated body corresponds to the diameter of the granulated body if it is spherical, and in the case of other shapes, when the granulated body is sandwiched between two parallel plates, The length of the part where the distance between the plates is the largest (the distance between the two plates) is indicated.

  Further, this granulated body preferably has a small particle size variation and a uniform particle size, and the uniformity coefficient (the sample particle size through which 60% of all samples pass in the sample particle size accumulation curve) The ratio of the particle diameter of the sample through which 10% passes is preferably 2 or less, particularly 1 to 1.5. In order to obtain a granulated body having a small uniformity coefficient in this way, it is preferable to perform a classification step of classifying the granulated body obtained by granulation according to a conventional method before or after drying.

[Drying process]
In the present invention, prior to firing the granulated product obtained in the granulation step, it is preferable to perform drying to volatilize and remove moisture in the granulated product. This drying is performed using a hot air dryer or the like. Thus, it is preferable to carry out at 80 to 180 ° C for about 0.5 to 3 hours.

[Baking process]
In the present invention, in the baking step, a preliminary baking step of baking at 200 to 300 ° C. and a main baking step of baking at 650 to 850 ° C. are performed, preferably as described above, from room temperature to 200 to 300 ° C. A primary temperature raising step for raising the temperature to a pre-baking temperature, a pre-baking step for firing at 200 to 300 ° C., and a secondary temperature raising from a pre-baking temperature of 200 to 300 ° C. to a main firing temperature of 650 to 850 ° C. A temperature raising step, a main baking step of baking at 650 to 850 ° C., and a temperature lowering step of lowering the temperature from the main baking temperature of 650 to 850 ° C. to room temperature. In addition, room temperature is a temperature of 5-45 degreeC normally.

<Baking atmosphere>
In the present invention, the firing is performed in an oxygen-containing atmosphere. If oxygen is not included in the firing atmosphere, it is impossible to oxidize and burn polymer alcohol as a plasticizer and to sinter clay as an aggregate.
The oxygen concentration in the firing atmosphere is preferably 10% by volume or more, particularly preferably 10% by volume or more in the combustion exhaust gas. Although there is no restriction | limiting in particular in the upper limit of the oxygen concentration in atmosphere, Usually, it is 25 volume% or less from the surface of work safety | security or cost. In general, firing in an air atmosphere, for example, under air circulation, is industrially advantageous because it does not require special oxygen supply means.

<Primary temperature raising step>
The primary temperature raising step for raising the temperature from room temperature to the pre-baking temperature is preferably performed at a temperature raising rate of 50 to 150 ° C./hr for about 1 to 3 hours. If the temperature increase time is short and the temperature increase rate is too fast, the crystal structure of the alkali metal titanate may be impaired. Conversely, if the temperature increase time is long and the temperature increase rate is too slow, the production efficiency decreases.

<Pre-baking step>
The pre-baking is performed in order to oxidatively decompose and remove the polymer alcohol in the granulated body. For complete combustion of the polymer alcohol, it is desirable to fire at a higher temperature. However, if the pre-baking temperature is too high, the heat generated by the oxidation reaction of the polymer alcohol in the granule causes the internal temperature of the granule to exceed the ambient temperature. As a result of the temperature becoming too high, the crystal structure of the alkali metal titanate may be impaired. However, since the combustion efficiency of the polymer alcohol is poor when the pre-baking temperature is too low, the pre-baking step is performed at a low temperature of 200 to 300 ° C, preferably 230 to 280 ° C.

  Although the time of this pre-baking process changes with pre-baking temperatures, it is preferable to carry out for 1-3 hours, especially about 1-2 hours. If the pre-baking time is too short, unburned polymer alcohol may remain. In addition, the pre-baking step is not required to be performed excessively long as long as the polymer alcohol is completely burned and removed.

<Secondary temperature raising process>
The secondary temperature raising step for raising the temperature from the preliminary firing temperature to the main firing temperature is preferably performed at a temperature raising rate of 50 to 150 ° C./hr for about 5 to 15 hours. That is, this firing step is a step for sintering the clay added as an aggregate at a temperature of 650 to 850 ° C. to give mechanical strength. At this time, the clay is a process of sintering. Shrinkage occurs. Therefore, if the polymer alcohol is burned and removed in the pre-baking step, if the temperature is rapidly raised to the sintering temperature, the granulated body may crack, and even if it does not crack completely, the granulated body is cracked. Then, sufficient mechanical strength cannot be imparted. Therefore, it is preferable that the secondary temperature raising step for raising the temperature from the pre-baking step at 200 to 300 ° C. to the main baking step at 650 to 850 ° C. is performed at an appropriate temperature raising rate within a range not impairing the production efficiency.

<Main firing process>
The main firing step of sintering the clay in the granulated body is performed at 650 to 850 ° C. If the firing temperature is less than 650 ° C, the clay cannot be sufficiently sintered to obtain an adsorbent with high mechanical strength. If the firing temperature exceeds 850 ° C, the crystal structure of the alkali metal titanate collapses and the adsorption performance decreases. To do. The preferred firing temperature is 700 to 850 ° C, preferably 750 to 800 ° C.

  Moreover, it is desirable that this firing time is about 1 to 3 hours in order to sufficiently sinter clay and obtain a high-strength adsorbent without impairing production efficiency.

<Cooling process>
As for the temperature lowering process for lowering the temperature from the main firing temperature to room temperature, the adsorbent may be broken if the temperature is lowered rapidly. Therefore, it is preferable to lower the temperature at an appropriate rate within a range not impairing the productivity. The temperature lowering step after firing takes 5 to 10 hours, and the adsorbent is cooled at a temperature lowering rate of about 100 to 250 ° C./hr to reach 90 to 110 ° C., preferably 95 to 105 ° C., for example, about 100 ° C. It is desirable to slowly cool at 10 to 30 ° C./hr.

<Baking means>
In the present invention, since the primary temperature raising, preliminary firing, secondary temperature raising, main firing, and temperature lowering steps as described above are performed with optimum temperature profiles, the firing temperature and firing time can be easily controlled. Firing is preferably performed using a firing furnace.

  Generally, when firing solid functional materials such as cement, ceramics, zeolites, solid catalysts, etc., electric tunnel furnaces, gas-fired tunnel furnaces, continuous rotary furnaces (kilns), batch-type rotary furnaces (kilns), fluidized bed firing furnaces A spray drying firing furnace is used, but for the firing of the adsorbent of the present invention based on an alkali metal titanate, an electric tunnel furnace, gas combustion capable of controlling the temperature and processing time of each step Firing is preferably performed while supplying an oxygen-containing gas using a type tunnel furnace, a batch kiln, or the like, and an electric tunnel furnace is particularly suitable.

  The electric tunnel furnace is to spread the material to be fired thinly into a slab and supply it into the tunnel furnace at a constant speed in a state where it is arranged on a belt conveyor. An electric heater is installed on the inner wall of the conveyor, which is divided into small parts in the moving direction of the conveyor. The temperature of each position in the moving direction can be set in advance and controlled to the set temperature while measuring the ambient temperature. Firing at temperature can be performed easily. Also, by spreading the material to be fired thinly in a bowl, the temperature difference between the surface and bottom of the material to be fired can be reduced, and firing can be performed under uniform conditions, resulting in adsorption The variation in performance for each particle of the agent can be reduced. Thus, when the granulated body is spread and fired in a thin layer in a mortar or the like, the thickness of the layer of this granulated body is preferably about 5 to 30 mm, particularly about 10 mm to 20 mm. Spreading in layers and firing is preferable because firing can be performed under uniform firing conditions.

[Strontium adsorbent]
The strontium adsorbent of the present invention produced through the above-described steps maintains the original crystal structure of the alkali metal titanate, exhibits high adsorption performance, and exhibits sufficient mechanical strength by clay sintering. Show. In particular, regarding the mechanical strength, the strength index (H) required for the activated carbon for water treatment described above is sufficiently satisfied, and therefore, it is crushed against physical stress applied during or before use as an adsorbent. Therefore, it is possible to prevent water passage troubles such as strainer blockage due to fine powder, and to prevent the problem of secondary contamination due to the outflow of fine powder adsorbing strontium.
In the strontium adsorbent of the present invention, the clay compounded as an aggregate is sintered in a state where the primary particles of the alkali metal titanate are crosslinked with each other. As a result, macropores of a crosslinked structure are formed in the adsorbent particles. This macropore contributes to the improvement of the diffusion rate of water to be treated in the particles, and can improve the adsorption performance and the treatment efficiency.

  The strontium adsorbent of the present invention is used, for example, by filling an adsorption vessel or adsorption tower having a strainer structure in the lower or upper part, and passing contaminated water containing strontium, particularly radioactive strontium, to the adsorption vessel or adsorption tower. The present invention can be effectively applied to a water treatment apparatus that removes strontium with water.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.

  In the following examples and comparative examples, the adsorption performance and mechanical strength of the produced adsorbents were evaluated by the following methods.

[Adsorption performance]
Batch adsorption where 1.5 g of adsorbent is added to 150 mL of test water with a NaCl concentration of 10,000 mg / L, Sr concentration of 0.1 to 3000 mg / L, Ca concentration of 10 mg / L, and Mg concentration of 1 mg / L and shaken for 48 hours. When the test was performed, the concentration of strontium in the test water when equilibrium was reached was C _eq [μg / mL], and the strontium adsorption amount per adsorbent unit weight at that time was q _eq [μg / mL]. K _d [mL / g] was determined.
K _d = q _eq / C _eq
The larger the distribution coefficient, the better the adsorption performance.

[Mechanical strength]
The strength index (H) [%] was determined according to the strength test method of JIS K1474 described above.

[Examples 1-6, Comparative Examples 1-4]
Potassium dititanate (K ₂ Ti ₂ O ₅ ) powder (average particle size 20 μm), clay (attapulgite), 7 wt% polyvinyl alcohol (PVA) aqueous solution, and additive (crystalline cellulose) in the following proportions The mixture was put into an extrusion granulator, kneaded and extruded into a columnar shape, and the columnar granulated product was formed into a spherical shape with a malmerizer. The obtained spherical granule was dried at 140 ° C. for 1.0 hour and then classified with a metal sieve to prepare an adsorbent precursor having an average particle size of 560 μm and a uniformity coefficient of 1.2.
Potassium dititanate powder: 100 parts by weight Clay: 21 parts by weight 7% by weight PVA aqueous solution: 83 parts by weight (PVA pure content: 5.8 parts by weight, water: 77.2 parts by weight)
Additive: 0.4 parts by weight

  The obtained adsorbent precursor was baked with a temperature profile shown in Table 1 below while supplying air using an electric tunnel furnace to obtain a strontium adsorbent. In the firing in the electric tunnel furnace, the adsorbent precursor was thinly spread and fired in a mortar to a thickness of 10 mm.

The obtained strontium adsorbent was examined for adsorption performance (partition coefficient (K _d )) and mechanical strength (strength index (H)), and the results are shown in Table 2.

As shown in Table 2, in the main firing step, sintering at a low temperature shows a higher distribution coefficient, and at 760 ° C. or lower, a substantially constant distribution coefficient is shown. When the temperature exceeded 840 ° C., the partition coefficient decreased rapidly, and at 900 ° C., the crystal collapsed, making it impossible to measure the partition coefficient.
On the other hand, the mechanical strength shows a high value when a high sintering temperature is adopted in the main firing step. It can be said that a sintering temperature of 650 ° C. or higher is necessary to maintain a strength index (H) of 80% or higher applicable as an adsorbent for water treatment.

[Example 7, Comparative Example 5]
50 mL of a strontium adsorbent (800 ° C. sintered product) produced in Example 4 was packed in a glass column having a column diameter of 8 mmφ (packed bed height: 100 mm), and raw water having the following water quality was passed under the following water flow conditions. A column flow test was performed (Example 7).
<Raw water quality>
NaCl: 10,000 mg / L
Sr: 45 mg / L
Ca: 20 mg / L
Mg: 5mg / L
<Water flow conditions>
Water flow rate: 50 mL / hr
Water passage speed (LV): 1 m / hr
Water flow space velocity (SV): 10 hr ⁻¹

  For comparison, a similar column water flow test was performed using A-type zeolite, which has high selectivity for strontium (Comparative Example 5).

The change with time of the strontium concentration of the treated water (column effluent) in each example was examined, and the results are shown in FIG.
The horizontal axis in FIG. 1 indicates a multiple of the accumulated water flow rate relative to the adsorbent filling capacity (Ratio to Bed Volume), and the vertical axis indicates the strontium concentration.

As shown in FIG. 1, in Comparative Example 5 using A-type zeolite, strontium was detected in the treated water from the beginning of water flow. On the other hand, in the adsorbent of Example 7 based on potassium dititanate, strontium was not detected in the treated water up to a water flow rate of 320 BV. In addition, the strontium concentration in the treated water is moderate in the A-type zeolite, whereas in the potassium dititanate granulated adsorbent of Example 7 manufactured using clay as an aggregate, the treated water strontium after breakthrough is used. The increase in concentration was fast.
The overall mass transfer capacity coefficient K _f a _v giving this breakthrough curve was determined from the following equation. Equation (1) is a Langmuir equation representing an equilibrium adsorption relationship using the distribution coefficient _Kd . Equation (2) is a column mass balance equation assuming a piston flow. By solving both, the overall mass transfer capacity coefficient K _f a _v was determined so as to reproduce the experimental value.

Here, C _eq : equilibrium solution concentration, q _eq : equilibrium adsorption amount, q _T : saturated adsorption capacity, C: Sr concentration in the liquid at the axial position z, C ^* : liquid in equilibrium with the adsorption amount at z Sr concentration, K _{f av} : overall mass transfer capacity coefficient, t: time, u: liquid superficial velocity, ε: porosity.
The adsorption characteristics of both are summarized in Table 3 below.

As shown in Table 3, saturated adsorption capacity q _T despite higher for A-type zeolite, the leakage strontium from water passing beginning is begun overall mass transfer and the low distribution coefficient K _d This is because the capacity coefficient K _f a _v is low. This is because if the overall mass transfer capacity coefficient K _f a _v is low, the length of the adsorption band becomes long and the effective utilization rate of the filled adsorbent decreases. Therefore, in the A-type zeolite of Comparative Example 5, the breakthrough curve is very broad. In contrast, in the potassium dititanate granulated adsorbent of Example 7, the distribution coefficient K _d and the overall mass transfer capacity coefficient K _f a _v are high, and the effective utilization rate of the adsorbent is high.

Claims (11)

  Mixing step of mixing alkali metal titanate powder with clay, polymer alcohol and water, granulating step of granulating the obtained mixture, and baking the obtained granulated body in an oxygen-containing atmosphere In the manufacturing method of the strontium adsorbent which has a baking process, this baking process includes the preliminary baking process baked at 200-300 degreeC, and the main baking process baked at 650-850 degreeC, The strontium adsorption | suction characterized by the above-mentioned Manufacturing method.   In Claim 1, it has a temperature rising process which heats up from the said pre-baking temperature to the said main baking temperature by the temperature increase rate of 50-150 degreeC / hr between the said pre-baking process and a main baking process, The firing step is performed for 1 to 3 hours, and the main firing step is performed for 1 to 3 hours. After the main firing, the temperature is lowered to a temperature of 90 to 110 ° C. at a temperature lowering rate of 100 to 250 ° C./hr, and then the temperature lowering rate of 10 to 30 ° C./hr. The method for producing a strontium adsorbent, characterized in that the temperature is lowered at a temperature.   3. The method for producing a strontium adsorbent according to claim 1, further comprising a drying step of drying the granulated body at 80 to 180 ° C. prior to the firing step.   The method for producing a strontium adsorbent according to any one of claims 1 to 3, wherein the firing in the firing step is performed in an electric tunnel furnace, a gas combustion tunnel furnace, or a batch rotary furnace.   The method for producing a strontium adsorbent according to any one of claims 1 to 4, wherein an oxygen concentration in the atmosphere in the firing step is 10% by volume or more.   In any 1 item | term of the Claims 1 thru | or 5, The said granule is a granular form with an average particle diameter of 150-3000 micrometers, arrange | positions this granulated body in the layer form of thickness 5-30mm, It is characterized by the above-mentioned. A method for producing a strontium adsorbent.   In any one of Claims 1 thru | or 6, 5-30 weight part of clay, 2-10 weight part of polymeric alcohol, and 50-120 weight part of water are mixed with respect to 100 weight part of alkali metal titanate powder. A method for producing a strontium adsorbent, comprising:   A strontium adsorbent produced by the method for producing a strontium adsorbent according to any one of claims 1 to 7.   An adsorption container filled with the strontium adsorbent according to claim 8.   An adsorption tower, which is packed with the strontium adsorbent according to claim 8.   A water treatment apparatus comprising the adsorption container according to claim 9 or the adsorption tower according to claim 10.

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