JPS61138530A - Inorganic cobalt adsorbent and its production - Google Patents

Abstract

PURPOSE:To prevent the shape crumbling of the titled adsorbent in under-water and to improve the maintenance of the mechanical strength by molding the cobalt adsorbent from a molded body of titania hydrate and/or titanium oxide contg. titania short fiber. CONSTITUTION:Titania sol is mixed uniformly and dispersively with a mixture of the titania short fiber and the titania particles and this mixture is molded. Then a titania cobalt adsorbent is produced by dehydrating the molded material at least partially. As the proportion of raw material of the titania short fiber, at least 2wt% expressed in terms of TiO2 is preferably for the raw material of total titania. Also as the added quantity of titania sol, 1-50wt% expressed in terms of TiO2 is preferable for the raw material of total titania. Alkali metal and alkaline earth metal capable of dissolving into high-temp. water are not necessarily contained in the raw material to the utmost.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an inorganic cobalt adsorbent and a method for producing the same. Specifically, the present invention relates to a titania-based cobalt adsorbent having excellent mechanical strength and hot water resistance and characterized by being made of a titania hydrate and/or titanium oxide molded body containing titania staple fibers. Furthermore, when manufacturing the above-mentioned titania-based cobalt adsorbent of the present invention, the steps of uniformly dispersing and kneading titania sol in a mixture of titania short fibers and titania particles, molding the mixed material, dehydrating the molded product under reduced pressure, The present invention relates to a method for producing a cobalt adsorbent made of a titania molded body, which comprises a step of at least partially dehydrating such as heating and dehydrating.

Although the inorganic cobalt adsorbent of the present invention is intended for a large amount of liquid to be treated, it can be effectively used as an adsorbent and remover for cobalt dissolved in the primary cooling water, which is a cause of radiation exposure in a Pushi reactor, for example.

The adsorbent of the present invention has excellent mechanical strength, adsorption ability, and hot water resistance, so it can be used under high temperature and high pressure without lowering the reactor water temperature. All reactor water purification systems that have been put into practical use for this purpose use organic ion exchange resins. However, since there is a problem with heat resistance, it is necessary to lower the temperature of water flowing to 60° C. or lower at the inlet of the purifier. In that case, in order to minimize thermal loss, only a portion of the total circulating water is cooled to a predetermined temperature and treated, and the remainder is left untreated.
Well, it gets recirculated. Therefore, its processing capacity and thermal efficiency are poor, and there is a strong demand for the development of an excellent inorganic ion adsorbent that can be used under high temperature and high pressure without lowering the reactor water temperature. , radiation-resistant inorganic ion adsorbents have been extensively studied.

It is known that compounds such as oxides and hydrous oxides of iron, tin, titanium, zirconium, manganese, niobium and tantalum, or salts of the above metals with phosphoric acid or tungstic acid are effective as inorganic adsorbents. . However, among the above-mentioned inorganic substances, when we comprehensively evaluate the cobalt adsorption characteristics, stability in i% hot water, and the difficulty of activating when a part of the adsorbent is brought into the reactor, , titanium oxide is preferred, and numerous methods have been proposed to put titanium oxide into practical use as an adsorbent.

For example, a method using powdered titanium oxide as an aggregate together with an agglomerated gold compound (%%
(Specification of Japanese Patent Publication), Adsorbent with titanium oxide supported by sintering on the surface of porous titanium metal (Specification of Japanese Patent Publication No. 59-62343), Adsorbent with titanium oxide supported on porous alumina (# (Japanese Patent Publication No. 57-40692).

All of these use titanium oxide as a cobalt adsorption active material, and there are problems with solid-liquid separation in practical use, and the need to maintain mechanical strength and use a porous carrier when used as a fixed bed. It is thought that the purpose of this is to improve the high dispersion of active substances and the mass transfer within the pores of cobalt, which is a non-adsorbent material.

However, all of the above-mentioned methods have problems in continuous operation, low adsorption capacity, and easy peeling of supported substances, and there are still many points that need to be improved before they can be used industrially.

On the other hand, it is known that titania hydrate fibers having a layered structure can be used as an ion exchange material by ion-exchanging H s O or H with Co'' in the layers (Ceramics, 19 (1984)). , No, 2.
P126-P133). Furthermore, titania hydrate fibers, amorphous titania fibers, and scales in which titania fibers are used as cation adsorbents are also known (Japanese Patent Laid-Open No. 55-337
1 publication specification). However, in both cases, there still remains a problem in the industrial continuous adsorption and separation of cobalt using only the fiber disclosed in the present invention. This is because the length of the titania-based fibers listed in the above-mentioned document is at most a few digits long (in the present invention, this shape is referred to as short fibers), so when their aggregates are dry, they are powder-like (1) When dispersed in water, it becomes a suspension and is essentially the same as titania particles. Therefore, when the above-mentioned titania fibers are used alone as an adsorbent, separation of solid and liquid is required as in the case of titania particles.

In addition, titania hydrate or titanium oxide can be used as a catalyst carrier,
Methods for producing molded bodies that can withstand industrial use as adsorbents have been studied for some time. For example, "a method of mixing an inorganic acid with a titanium water-use oxide having a natase type or amorphous crystal structure and molding it" (Japanese Patent Application Laid-open No. 55-8844
(specification of the publication), adding fine particle silicic acid to titanium sulfate,
A method of calcining after thermal hydrolysis (Japanese Patent Application Laid-Open No. 59-35025, etc.), a method of peptizing a part of Iruri titanium and calcining,
Examples include a two-stage firing method (Japanese Patent Laid-Open No. 123532/1983) in which titania sol is added to pulverized powder and molded.

However, when these are used for high-temperature, high-pressure treatment of nuclear reactor water, their strength and cobalt adsorption performance are still unsatisfactory.

In addition, especially if the binder used to increase the strength of the molded product contains a metal component other than titanium that is easily affected by radiation, that component will peel off during the above treatment and become radioactive. There is a danger that

Furthermore, even if the above-mentioned known techniques are applied to only short titania fibers or a mixture of short titania fibers and titania particles, the mechanical strength and hot water resistance will be insufficient, such as disintegration in water.

<Problems to be Solved by the Invention> Although the titania-based adsorbent of the prior art described above has been put into practical use as an adsorbent for cobalt in nuclear reactor-fire reactor water, it is difficult to effectively separate it from reactor water.

■Those with titania hydrate or titanium oxide supported on a porous carrier have insufficient titania content, which is the adsorption active ingredient, and cannot be compressed, resulting in a large decrease in adsorption capacity and the titania component easily peeling off. . ■ Molded titania hydrates or titanium oxides have unsatisfactory points such as mechanical strength, hot water resistance, reduced adsorption ability due to low surface area, and adverse effects due to impurities mixed in during molding.

Means for Solving the Problems> The present invention has been made in view of the above problems, and provides a substantially titanium hydrate and/or material having excellent cobalt adsorption ability under high temperature and pressure, mechanical strength, and hot water resistance. Alternatively, a titania molded body made of an oxide is provided.

That is, the present invention is specified as follows.

(1) A titania-based cobalt adsorbent comprising a titania hydrate and/or titanium oxide molded body containing titania staple fibers.

(2) Titania short fibers have a diameter of 0.1 μm ~ 1) I!
Adsorbents in the l+ range.

(3) The content of titania short fibers is TiO2 relative to the total titania hydrate and/or titanium oxide in the molded body.
The adsorbent according to (1) or (2) above, wherein the adsorbent is at least 2] Li%.

(4) Consists of a step of uniformly dispersing and kneading titania sol in a mixture of titania staple fibers and titania particles, a step of molding the resulting kneaded product, and a step of at least partially dehydrating the resulting molded product. A method for producing a titania-based cobalt adsorbent characterized by:

(5) The method according to (4) above, wherein the raw material proportion of the titania short fibers is at least 2% by weight as TiO2 based on the total titania raw material.

(6) The method described in (4) or (5) above, wherein the amount of titania sol added is in the range of 1 to 50% by weight of TiO2 based on the total titania raw material.

<Function> It is known that an inorganic oxide sol serves as a binder for an inorganic molded body. However, according to studies conducted by the present inventors, when producing a titania molded article containing short titania fibers, silica sol or alumina sol hardly exhibits a binder effect when added in small amounts. Surprisingly, when titania sol is used, a remarkable binder effect is exhibited even with the addition of a small amount, and at the same time, mechanical strength and hot water resistance are improved, and the cobalt adsorption ability is extremely excellent. I learned something I couldn't have known. On the other hand, when titania particles are used as raw material and similarly molded with titania sol, the binder force is weak and a large amount of sol is required or a complicated process as shown in, for example, the specification of Japanese Patent Publication No. 59-123532 is required. It is presumed that the addition of titania short fibers and the use of titania sol in the present invention work synergistically, and for the first time, a molded body suitable as an adsorbent can be obtained.

The titania short fibers used in the present invention are produced by a conventionally known manufacturing method, and their shapes range from 0.1 μm to 11 mm in diameter.
11), the length is in the range of 0.5 μm to 5 wm, and preferably the aspect ratio is 3 or more, and particularly preferably the aspect ratio is 5 or more. These 4, for example, general formula M z O
・Production method of titania fiber from alkali metal titanate whiskers represented by 1TiQ2 (M is an alkali metal, and n is a positive number in the range of 1 to 6) by hydrothermal treatment or water sprinkling #liquid treatment (Shigyo Kyokai Magazine, 86 [c+] 1
97 s.

P430 to P432, % Japanese Patent Application Publication No. 55-3371, Japanese Patent Application Publication No. 59-150543, etc.), Section 3.

A method of gradually oxidizing a titanium oxide solution with an oxidizing gas (Japanese Unexamined Patent Publication No. 56-78426), a method of acid treatment of a composite of titanium alkoxides and potassium hydroxide after spinning (
JP-A-58-156347), a method of adding an oxide aqueous titania sol into a heated heat medium solution (
JP-A-58-174618). If the shape is within the above-mentioned range, it can be used as the short titania fiber in the present invention. Crystalline forms include titania hydrate, amorphous, and anatase.

It may be any or a mixture of titanium oxides such as rutile.

The addition ratio of titania short fibers to the titania raw material is effective in improving mechanical strength and water resistance when combined with the addition of titania sol, but it is preferable that the content of titania short fibers is low enough to improve the molded product. At least 2 weights of titania hydrate and/or titanium oxide, calculated as T i Oz, are used. If it is less than 2%, the effect of its addition is not sufficient. In addition, as an example within the above range, it is naturally included that a molded body is made by adding titania sol to the raw material of only titania short fibers, and in this case, in addition to having the percentage characteristics disclosed in the present invention as shown in the examples,
It is a particularly preferred adsorbent from the viewpoint of improving adsorption efficiency since the pore diameter is very controlled within a certain range. The pore size has a correlation with the shape of the titania short fibers used, especially the diameter.If a large number of small pores are required, the proportion of short fibers with small diameters should be increased, and conversely, many large pores are required. In this case, the pore size and pore size distribution can be freely controlled by mainly using short fibers with a large diameter. It is preferable that the content of the titania short fibers is more than 60% by weight of TiOx based on the titania compound in the molded body, since the physical properties of the side holes can be controlled. % mentioned above
This feature is advantageous in that when it is put to practical use as an adsorbent, it is possible to produce an adsorbent that can respond to the adsorption operation conditions such as the flow rate and temperature of the p-liquid by controlling the mass transfer in the molded body. Moreover, the effect of removing crud contained in cool oven cooling water is also increased, which is preferable. However, it is clear that the above-mentioned advantages only indicate additional characteristics when titania short fibers are contained within a certain range, and do not limit the content of titania short fibers.

Particulate raw materials of titania hydrate and/or titanium oxide other than titania short fibers and titania sol (simply referred to as titania particles) are spherical, irregularly shaped, or agglomerated particles/particles, acicular or rectangular in shape. All titanium raw materials that can be converted into titania hydrate and/or titanium oxide when applied with an ik terminal agent other than titania short fibers and titania sol, such as particles with an aspect ratio of less than 3, even if they are Include. They are manufactured by conventionally known methods. Orthotitanic acid and metatitanium obtained by alkaline hydrolysis, thermal hydrolysis, etc. of titanium salts such as titanium tetrachloride, titanyl sulfate, and titanium nitrate, or by hydrolyzing titanium alkoxides such as titanium tetraisopropoxide. These include titania hydrates such as acids, and amorphous, anatase-type, or rutile-type titanium oxides that are obtained by calcining titania hydrates.

Furthermore, it is also possible to use the above-mentioned short titania bond fibers which are mechanically powdered to have an aspect ratio of less than 3.

Titania sol can also be produced by a conventionally known method. For example, after hydrolyzing titanium salts such as titanium tetrachloride and titanyl sulfate to form orthotitanic acid particles, peptizing them with barium chloride or hydrochloric acid, or partially converting titanium alkoxides such as titanium tetraisopropoxide into orthotitanic acid particles. Although it can be produced by a method such as hydrolysis, it is not limited to the above production method t'c. As the titania sol, either an aqueous sol in which the solvent is water-based or an organosol in which the solvent is an organic solvent such as alcohols such as ethanol and isopropanol, or aromatics such as toluene can be used.

The titania sol referred to in the present invention may have a size distribution of the titania single particles constituting the sol, but when indicating the amount of titania sol added, the size of the single particle is 1.
The amount of particles within the range of 0 to 1,000 is expressed in terms of Ti0z.

This is because, according to the findings of the present inventors, the size of a single titania particle is 10~t, oooλ, more preferably 30~
This is because titania particles within the range of 5ooX are highly effective as a binder. Therefore, particles with a single particle diameter outside the above range are treated as titanium di'γ hydrate particle raw materials.

The amount of titania sol added is TiO2 for the total titania i material.
It is preferably added in a range of 1 to 5039J1%.

If it is less than 1 qh, it will not be possible to obtain a molded product that has the mechanical strength and hot water resistance required for opening according to the present invention, and if it is more than 50%, the binder force will increase, but this is not economical.

Metal compounds such as alkali metals and alkaline earth metals, and compounds such as sulfur and norogen, which may be leached out in high-temperature water, and compounds such as sulfur and norogen should not be contained in each of the above titania raw materials as much as possible.

If there is a collapse, there will be a problem of corrosion of pipes and other parts due to these substances leaching into the reactor water.

First, titania sol and optionally an appropriate amount of water, alcohol, etc. are added to a mixture of titania short fibers and titania particles, or a raw material of only titania short fibers, and the titania sol is uniformly dispersed and kneaded.

In this case, a commonly used moldability improver such as starch or polyvinyl alcohol may be added to the mixed material in consideration of moldability in the subsequent molding step. Further, in order to further increase the mechanical strength, whiskers such as silicon carbide, silicon nitride, and alumina may be contained in a range of 1 to 30 iJi%.

Next, the kneaded product is made into a molded product by a conventionally known method such as extrusion molding, transfer granulation, tablet molding, or marmerizer molding.

The molded product can be molded into any shape such as a pellet, sphere, rod, triangular pyramid, ring, or honeycomb shape.

The molded product is then at least partially dehydrated to form an adsorbent. Specifically, it can be appropriately selected from methods such as room temperature drying, vacuum dehydration, and heating dehydration. The choice of dehydration method depends on the chemical properties of titanium as an adsorbent.
% is related to crystal structure. For example, when producing an adsorbent consisting only of titania hydrate, it can be obtained by drying at room temperature and/or dehydration under reduced pressure at 0 to 200°C. In the case of production, heating dehydration up to 1100° C. can be carried out alone or subsequent to room temperature drying and/or vacuum dehydration. In the case of other crystal forms and mixtures, dehydration can be carried out by any one of the above three methods or in combination.

The titania sol can be effectively used as a binder only through the dehydration process described above.

The mechanism is thought to be that the hydroxyl groups on the surface of the sol particles in the titania sol strengthen the molded product through dehydration condensation with the hydroxyl groups on the surface of the sol particles, short titania fibers, and titania particles. Among these, something that the present inventors could not have expected was that room temperature drying and/or
It has excellent hot water resistance at low temperatures such as normal pressure or vacuum dehydration at 200°C, and therefore, it is possible to produce an adsorbent that can withstand practical use regardless of the structure of titanium.

The molded adsorbent produced using the raw materials and manufacturing method described above is used by providing a reactor water purification system in a primary reactor water system such as a water supply system or a boat circulation system in a light water reactor and filling the system with the adsorbent. In that case, there is no need to lower the reactor water temperature (280-3zoc) before the purification system.

The present invention will be explained in more detail with reference to Examples below.

In addition, each physical property measurement was performed by the following method.

Mechanical strength: 0 crushing strength - 0 by Kiya type hardness tester - Powdering degree: 100 - Molded adsorbent lr (4 mφ x 4ffi1) (approximately 20 IH pellets) and pure water 50 m / Prepare 10 flasks.
After rotating at Or, p, m for 1 hour, the molded body was taken out, dried, and weighed according to the following formula.

Hot water resistance 0 Deformation in high-temperature water - Visual observation of the molded body after cobalt adsorption test in high-temperature water and confirmation of water turbidity 0 Elution of titanium into water - Deformation in water after cobalt adsorption test in high-temperature water Titanium was measured by atomic absorption spectrometry.

Other physical properties: 0 surface area - 0 pore volume by BET method, pore size distribution - Example 1 by mercury intrusion method
~7 (1) Production of titania short fiber Potassium tetratitanate short fiber (diameter 0.2-0.7t1m
+ length 3 to 500 μm) was suspended in a 0.5N nitric acid aqueous solution, stirred at room temperature for 12 hours, and then separated from the liquid by filtration. Repeat the above operation three times and finally wash the cake with pure water. Elute and remove the potassium ions in the potassium tetratitanate short fibers to obtain titania hydrate whiskers, and then bake at 300°C to create titania short ffl. # (titania short fibers - number 8) was produced. Shape of the titania short fibers (observation results using an electron microscope), T i Oz content i
1 (the remainder is hydration water) is shown in Table 1 below. Potassium tetratitanate short li1. Various short titania fibers were produced using titania fibers as raw materials and varying the degree of burning resistance. Table 1 below shows the manufactured titania short NR fiber numbers and physical properties.

Table 1 Note that the impurity metal in the titania short fibers was only potassium with a slight Ik (less than 0% by weight), and all the aspect ratios of the shapes were 5 or more.

(n) Production of titania sol Production method 1 A titanyl sulfate aqueous solution and aqueous ammonia were added to form a precipitate of orthotitanic acid, and the precipitate was separated and washed with a large amount of water to obtain a cake of orthotitanic acid. Next, dissolve concentrated nitric acid in water (molar ratio of nitric acid to Ti1t in the cake: 2.5)
The cake was added to stirring F to obtain a transparent crude titania sol. Next, the sulfate ions and nitrate ions contained in the crude titania sol were removed by dialysis to produce a pure titania sol (15 weight as Ti12). The size of the titania particles in the titania sol was determined to be within the range of 60 to 150λ as a result of observation using a transmission electron microscope. (Assumed to be in titania sol) 0 Manufacturing method 2 While stirring an IN nitric acid aqueous solution, an inpropatol solution of titanium tetraisogloboxoxide was gradually dropped into it to form a quantum titania sol with a Ti0t equivalent concentration of 2.0. Then, a part of the solvent (Ingropanol) was evaporated at room temperature under reduced pressure to produce a titania sol containing 8.5% by weight of TiOz-exchanged X* degree. The size of titania particles in the sol was 500-800λ. (Titania Solurotosul) (1) Production of adsorbent (titania short fibers and particulate titanium oxide (manufactured by Degup Aerosil Titanium Oxide P-25 Anatase/Rutile = 75/25,... Particulate titanium oxide (X) or titania short fibers: mechanically crushed O01-i, oμm dog rectangular titania particles (aspect ratio less than 3)...particles titanium oxide (Y
) in a blender, mix thoroughly, then add (1
) was added, uniformly dispersed, and kneaded.

Next, push out the above-mentioned contaminants and place them on a molded rock.
w H was extruded and molded into pellets. Next, the molded bodies were dehydrated under the conditions shown in ff-2 below to produce various titania molded adsorbents. Table 2 shows the relationship between the adsorbent number, the raw material ratio of Ti1t, and the physical properties of the adsorbent.
-'Mo#/1) 100t/and approximately 0.22 of the adsorbent manufactured by (Ayame) were weighed, and 500-mm stainless steel (S
US-31s) was placed in an autoclave and heated from the outside to bring the internal liquid temperature to 320°C. The sample water and adsorbent were taken out, and the sample water was checked for turbidity due to deformation of the adsorbent and T by atomic absorption analysis.
Measure the solution of t=i, and for the adsorbent, add ammonium +11C acid, which has been thoroughly washed with water, dissolve Absorbent 1 in filtered sulfuric acid, and analyze the amount of cobalt in the solution by atomic absorption spectroscopy. The cobalt adsorption ikt was determined by this method.The results are shown in Table 3 below.

Claims (6)

[Claims] (1) A titania-based cobalt adsorbent comprising a titania hydrate and/or titanium oxide molded body containing titania staple fibers. (2) Claim (1) characterized in that the titania short fibers have a diameter in the range of 0.1 μm to 1 mm, a length in the range of 0.5 μm to 5 mm, and an aspect ratio of 3 or more.
Adsorbent as described. (3) Claim (1) or (2) characterized in that the content of titania short fibers is at least 2% by weight as TiO_2 based on the total titania hydrate and/or titanium oxide in the molded body. ) adsorbent described. (4) Consisting of a step of uniformly dispersing and kneading titania sol in a mixture of titania staple fibers and titania particles, a step of molding the resulting kneaded product, and a step of at least partially dehydrating the resulting molded product. A method for producing a titania-based cobalt adsorbent characterized by: (5) The method according to claim (4), wherein the raw material proportion of the titania short fibers is at least 2% by weight as TiO_2 based on the total titania raw material. (6) The amount of titania sol added is T to the total titania raw material.
The method according to claim (4) or (5), characterized in that iO_2 is 1 to 50% by weight.