JP6779768B2 - Adsorbent containing amorphous iron (III) hydroxide and its production method - Google Patents

Description

The present invention particularly relates to an adsorbent having excellent iodine ion adsorption performance and a method for producing the same.

Radioiodine emitted from nuclear facilities is said to be of three types: iodine (I ₂ ), hydroiodic acid (HI) and methyl iodide (CH ₃ I).

The following methods are used as methods for removing these radioactive iodines.
(1) A method in which an iodine-containing gas or liquid is brought into contact with silver zeolite and collected as silver iodide.
(2) A method of collecting radioactive iodine (iodine-131) by isotope exchange with non-radioactive iodine using a large amount of impregnated activated carbon impregnated with potassium iodide.
(3) A method for removing an iodine-containing gas or liquid by contacting it with an ion-exchangeable fiber having an amino group.
(4) A method for adsorbing iodine using insoluble cyclodextrin or a derivative thereof as an active ingredient.
(5) A method of adsorbing iodic acid using cerium hydroxide as an adsorbent.

A method of using iron (III) hydroxide as an adsorbent has also been proposed.
Non-Patent Document 1 proposes to remove iodic acid ions by coprecipitating iron (III) hydroxide produced by adding iron (III) nitrate and sodium hydroxide to a solution containing iodic acid ions. ing.
Further, in Patent Document 1, an aqueous solution containing iron ions is neutralized with an alkali to form a precipitate, the precipitate is washed with deionized water, and dried iron (III) hydroxide is used as an adsorbent. Proposed.

Japanese Unexamined Patent Publication No. 2016-12302

RADIOISOTOPES, 51, 149-156, 2002

Recently, in addition to iodine, hydroiodic acid, and methyl iodide, the removal of iodic acid (IO ₃ ) ions has become a problem. This is because sodium hypochlorite is used in the process of treating contaminated water from the nuclear power plant, so iodine ions in the contaminated water are oxidized by sodium hypochlorite to generate iodic acid ions. It is presumed to be.

Inorganic adsorbents such as silver zeolite and cerium hydroxide are excellent in adsorbing performance of iodic acid ions, but they are expensive and not industrially advantageous.

Although iron (III) hydroxide is an inexpensive material, it is required to further improve its adsorption performance for iodic acid ions and the like.

For example, radioactive substances discharged from a nuclear facility are adsorbed and removed by a water treatment system having a column (adsorption tower) filled with an adsorbent for radioactive substances.

In Non-Patent Document 1 relating to a conventional adsorbent for iron (III) hydroxide, iodic acid is used for co-precipitating and removing iodate ions in iron (III) hydroxide generated from a solution containing iodate ions. Although the conditions on the solution side containing ions are being investigated, no study has been made on the technology of the adsorbent used by recovering the iron (III) hydroxide from the reaction solution and filling it in a column or the like.

In addition, as the adsorbent used by filling the column or the like, a granulated product is usually used, but an adsorbent obtained by granulating iron (III) hydroxide using a binder is applied to remove iodic acid ions. Then, the adsorption performance for iodate ions tends to decrease due to the binder component. Further, the adsorbent in which iron (III) hydroxide is supported on other inorganic materials and organic materials has a problem that the adsorption performance is lowered because the content of iron (III) hydroxide as an active ingredient is low. is there.

Therefore, an object of the present invention is an adsorbent containing iron (III) hydroxide, which can be used even when packed in a column or the like and has excellent adsorption performance of iodic acid ions, and an industrially advantageous production method thereof. Is to provide.

As a result of diligent research in view of the above circumstances, the present inventors have a specific range of the temperature of the exothermic peak appearing on the DSC temperature rise characteristic curve in the temperature rise process of 25 to 700 ° C, and the temperature rises to 25 to 700 ° C. By obtaining amorphous iron (III) hydroxide having a weight loss rate of more than a specific value and an electrical conductivity of less than a specific range, the adsorption performance of iodic acid ions is particularly excellent, and the binder is also used. To become amorphous iron hydroxide (III) that can be granulated without using. Further, they have found that the amorphous iron (III) hydroxide is particularly excellent in the adsorption performance of iodic acid ions even when used as a granulated product, and have completed the present invention.

That is, the adsorbent to be provided by the present invention has an exothermic peak temperature of 350 to 400 ° C. that appears on the DSC temperature rise characteristic curve in the temperature rise process of 25 to 700 ° C., and the temperature rises to 25 to 700 ° C. It is characterized by containing amorphous iron (III) hydroxide having a weight loss rate of 18% or more and an electric conductivity of 14 mS / cm or less.

Further, the method for producing an adsorbent to be provided by the present invention is to prepare a slurry containing iron (III) hydroxide by performing a neutralization reaction between an iron mineral salt and an alkali hydroxide in an aqueous solvent. One step, the second step of aging the slurry at pH 3.0-5.0, then washing with water until the electrical conductivity of the 10 mass% slurry containing iron (III) hydroxide is 14 mS / cm or less. It is characterized by having a third step, and then a fourth step of extrusion-molding the water-containing iron (III) after the washing treatment and drying the obtained molded product at 150 ° C. or lower.

According to the present invention, it is possible to provide an adsorbent containing amorphous iron (III) hydroxide, which can be used even if it is packed in a column or the like and has particularly excellent adsorption performance for iodate ions. , Amorphous iron hydroxide (III) effective as the adsorbent can be produced by an industrially advantageous method.

X-ray diffraction pattern of amorphous iron (III) hydroxide obtained in Example 1. X-ray diffraction pattern of amorphous iron (III) hydroxide obtained in Example 2. The DSC temperature rising characteristic curve of amorphous iron (III) hydroxide obtained in Example 1. FIG. The DSC temperature rising characteristic curve of amorphous iron (III) hydroxide obtained in Example 2. FIG. The DSC temperature rising characteristic curve of amorphous iron (III) hydroxide obtained in Comparative Example 1. The DSC temperature rising characteristic curve of amorphous iron (III) hydroxide obtained in Comparative Example 2. The figure which shows the result of the column test using the amorphous iron (III) hydroxide obtained in Example 2 as an adsorbent.

Hereinafter, the present invention will be described based on the preferred embodiment thereof.
The adsorbent according to the present invention contains amorphous iron (III) hydroxide. The amorphous iron (III) hydroxide used as the adsorbent of the present invention may be a powder, or may be granulated particles obtained by granulating the powder, or a mixture thereof. May be good.
The powder referred to here preferably has a median diameter D50 of 1 to 100 μm according to a laser diffraction / scattering type particle size distribution method.

The amorphous iron (III) hydroxide used as an adsorbent in the present invention is preferably a granulated product from the viewpoint of filling the column and using it. The particle size of the granulated product is preferably 200 to 1000 μm, more preferably 300 to 600 μm. Specifically, when a sieve having a mesh size of 212 μm and a sieve having a mesh size of 1 mm according to the JIS Z8801-1 standard are used, 98% by mass or more of the adsorbent, particularly 99% by mass or more, passes through the sieve having a mesh size of 1 mm. It is preferable that 98% by mass or more, particularly 99% by mass or more, does not pass through a sieve having an opening of 212 μm. As described above, when the adsorbent of the present invention has a small particle size of less than 212 μm, it is preferable to fill the adsorbent with the adsorbent and pass water through the adsorbent because the powder is less likely to be clogged in the adsorbent. Further, when the adsorbent of the present invention has a small particle size of more than 1 mm, the adsorbent has a high adsorbing ability and the overall adsorbing performance can be improved, which is preferable. In particular, when a sieve having a mesh size of 300 μm and a sieve having a mesh size of 600 μm according to the JIS Z8801-1 standard are used, 98% by mass or more of the adsorbent, particularly 99% by mass or more, passes through the sieve having a mesh size of 600 μm and 98% by mass. As described above, it is particularly preferable that 99% by mass or more does not pass through a sieve having an opening of 300 μm.

As the amorphous iron (III) hydroxide used in the adsorbent of the present invention, one having an exothermic peak temperature of 350 to 400 ° C. appearing on the DSC temperature rising characteristic curve in the heating process of 25 to 700 ° C. is used. There is one of the features in particular.

In the amorphous iron (III) hydroxide used in the adsorbent of the present invention, the reason why the temperature of the exothermic peak is set in the above range is that the adsorption performance of iodic acid ion is particularly low when the temperature of the exothermic peak is not in the above range. This is because the granulation process becomes difficult. Further, the amorphous iron (III) hydroxide used in the adsorbent of the present invention preferably has an exothermic peak of 370 to 400 ° C., particularly from the viewpoint of further improving the adsorption performance of iodic acid ions. It is particularly preferable that the temperature is 370 to 390 ° C.

One of the features of the amorphous iron (III) hydroxide used in the adsorbent of the present invention is that the weight loss rate when the temperature rises to 25 to 700 ° C. is 18% or more.

In the amorphous iron (III) hydroxide used in the adsorbent of the present invention, the reason why the weight loss rate when the temperature rises to 25 to 700 ° C. is within the above range is that the weight loss rate is not in the above range. This is because the adsorption performance of iodic acid ions is low.
In the present invention, the weight loss rate when the temperature is raised to 25 to 700 ° C. is preferably 18 to 35%, more preferably 18 to 30%, particularly from the viewpoint of improving the adsorption performance of iodic acid ions.

One of the features of the amorphous iron (III) hydroxide used in the adsorbent of the present invention is that it has the above physical properties and also has an electric conductivity of 14 mS / cm or less.

According to the present inventors, a granulated product having excellent adsorption performance by using an amorphous iron (III) hydroxide having an electric conductivity of 14 mS / cm or less for granulation treatment. I found that it would be. In the present invention, the electrical conductivity of amorphous iron (III) hydroxide is preferably 12 mS / cm or less, particularly preferably 10 mS / cm or less, from the viewpoint of producing a granulated product having excellent adsorption performance. preferable.

In the present invention, the electric conductivity means the electric conductivity when a 10% by mass slurry is prepared in water at 25 ° C.
The electrical conductivity is a value caused by ionic impurities such as halogen ions, sulfate ions, nitrate ions, ammonium ions, and alkali metal ions contained in the amorphous iron hydroxide (III).

The amorphous iron (III) hydroxide used in the adsorbent of the present invention has the above physical properties and a BET specific surface area of 100 to 300 m ² / g, preferably 150 to 300 m ² / g, more preferably. Is preferably 200 to 300 m ² / g, particularly from the viewpoint of improving the adsorption performance of iodic acid ions.

The amorphous iron hydroxide (III) according to the adsorbent of the present invention contains, for example, iron (III) hydroxide obtained by performing a neutralization reaction between an iron mineral salt and an alkali hydroxide in an aqueous solvent. The first step of preparing the slurry, the second step of aging the slurry at pH 3.0 to 5.0, and then until the electrical conductivity of the 10 mass% slurry containing iron (III) hydroxide becomes 14 mS / cm or less. Manufactured by having a third step of washing with water, and then a fourth step of extrusion-molding the hydrous iron (III) after the washing treatment and drying the obtained molded product at 150 ° C. or lower. What is preferred.

Hereinafter, a method for producing an adsorbent according to the present invention will be described.
The first step is a step of preparing a slurry containing iron (III) hydroxide by performing a neutralization reaction between an iron mineral acid salt and an alkali hydroxide in an aqueous solvent.

Examples of the iron mineral acid salt according to the first step include iron (III) chloride, iron (III) sulfate, iron (III) nitrate and the like.
The iron mineral acid salt is used as an aqueous solution in which the iron mineral acid salt is dissolved in water. The concentration of the aqueous solution containing the iron mineral acid salt is 1 to 50% by mass, preferably 10 to 45% by mass.

Examples of the alkali hydroxide according to the first step include sodium hydroxide, potassium hydroxide, lithium hydroxide, aqueous ammonia and the like.
Alkali hydroxide is used as an aqueous solution in which alkali hydroxide is dissolved in water. The concentration of the aqueous alkali hydroxide solution is 1 to 50% by mass, preferably 5 to 25% by mass.

The operation method of the neutralization reaction in the first step is not particularly limited, and an aqueous alkali hydroxide solution and an aqueous solution containing an iron mineral acid salt may be brought into contact with each other. For example, (1) a method of adding an aqueous solution containing an iron mineral salt to an aqueous solution of an alkaline hydroxide to perform a neutralization reaction, and (2) adding an aqueous solution of an alkaline hydroxide to an aqueous solution containing an iron mineral salt to neutralize Examples thereof include a method of carrying out the reaction and (3) a method of simultaneously adding an aqueous solution containing an aqueous alkali hydroxide solution and an aqueous solution containing an iron salt salt to an aqueous solvent to carry out a neutralization reaction.
In this production method, the contact method between the alkaline hydroxide aqueous solution and the aqueous solution containing the iron mineral acid salt is performed by the method (1) above, from the viewpoint that a product having good yield and excellent adsorption performance can be obtained. preferable.

Addition of an aqueous solution containing an iron mineral acid salt and / or an aqueous alkali hydroxide solution may cause iron (III) hydroxide to crystallize and the adsorption performance to deteriorate when the reaction temperature is high. It is preferably performed at 70 ° C. or lower, more preferably 10 to 70 ° C.

The rate of addition of the aqueous solution containing iron mineral salt or the aqueous alkali hydroxide solution is not particularly limited, but it is possible to obtain a stable quality by adding the solution to the other solution so that the rate is constant. Preferred from the point of view.

The slurry containing iron (III) hydroxide after the completion of the first step is subjected to the second step and aged.

The second step is a step of adjusting the pH of the slurry containing iron (III) hydroxide obtained in the first step and aging it.

In the method for producing this adsorbent, by performing this second step, the adsorption performance of iodic acid ions is particularly excellent, and the amorphous treatment can be performed by a synergistic effect with the cleaning treatment of the third step described later. Quality iron (III) hydroxide can be produced.

In the second step, it is important to adjust the pH of the slurry containing iron (III) hydroxide obtained in the first step to 3.0 to 5.0 for aging. The reason for this is that in the second step, if the pH of the slurry containing iron (III) hydroxide is not in the above range, the adsorption performance of iodic acid ions is particularly inferior, and the granulation treatment becomes difficult. In the present invention, the second step is a slurry containing iron (III) hydroxide from the viewpoint of obtaining amorphous iron (III) hydroxide which is particularly excellent in adsorption performance of iodic acid ions and can be granulated. The pH of is preferably adjusted to 4.0 to 5.0.

In the second step, if necessary, the pH of the slurry containing iron (III) hydroxide obtained after the first step can be adjusted using an acid or an alkali.

The aging temperature according to the second step is preferably 90 ° C. or lower, preferably 70 ° C. or lower, and more preferably 10 to 70 ° C. from the viewpoint of preventing crystallization of iron (III) hydroxide. The aging time according to the second step is 1 hour or more, preferably 1 to 12 hours.

The slurry containing iron (III) hydroxide that has been aged in the second step is subjected to a cleaning treatment in the third step.

In the third step, the iron (III) hydroxide aged in the second step is washed and the electric conductivity of the 10 mass% slurry containing the iron (III) hydroxide is 14 mS / cm or less, preferably 12 mS / cm. This is a step of sufficiently washing with water until the size becomes cm or less.

In the method for producing this adsorbent, in addition to the above-mentioned second step, ionic impurities such as halogen ion, sulfate ion, nitrate ion, ammonium ion and alkali metal ion are removed from iron (III) hydroxide in this third step. By doing so, it is possible to obtain amorphous iron (III) hydroxide that can be granulated while maintaining the excellent adsorption performance of iron (III) hydroxide.

The method for cleaning iron (III) hydroxide in the third step is not particularly limited, but it is particularly preferable to use iron (III) hydroxide by means such as repulp.

The washed iron (III) hydroxide obtained after the third step is subjected to the fourth step in a water-containing state for granulation treatment.

In the fourth step, the water-containing iron (III) hydroxide that has been washed after the third step is extruded to obtain a molded product, and the molded product is dried to obtain an amorphous iron hydroxide (III). ) Is a step of obtaining an adsorbent containing.

The water content of iron (III) hydroxide in a water-containing state is 40 to 60% by mass, preferably 45 to 55% by mass, which is contained in iron (III) hydroxide in advance when the granulation treatment is performed. It is preferable to use the adjusted product from the viewpoint of suppressing the generation of unmolded products and obtaining a molded product in good yield.

The water content of iron (III) hydroxide in a water-containing state can be adjusted by, for example, suction filtration, centrifugation, filter press, natural drying, blast drying, freeze drying, hot air drying, or the like.

In the fourth step, first, the hydrous iron (III) hydroxide is extruded from the perforated member in which a plurality of perforations are formed to obtain a molded product.

Examples of the shape of the hole formed in the opening member include a circle, a triangle, a polygon, and a ring shape. The perfect circle equivalent diameter of the hole is preferably 0.1 mm or more and 10 mm or less, and more preferably 0.3 mm or more and 5 mm or less. The perfect circle conversion diameter referred to here is the diameter of a circle calculated from the area when the area of one hole is taken as the circle area.

In this production method, it is important that the molded product obtained after extrusion molding is dried at 150 ° C. or lower.

According to the present inventors, it has been found that the temperature at which the molded product is dried also affects the adsorption performance of iodic acid ions and the like.
In this manufacturing method, the reason why the drying temperature of the molded product is within the above range is that when the drying temperature of the molded product exceeds 150 ° C., the surface hydroxyl groups that contribute to adsorption become remarkable, and sufficient adsorption performance is not exhibited. Is. Further, in the present production method, the drying temperature of the molded product is preferably 80 to 150 ° C., more preferably 80 to 120 ° C., particularly from the viewpoint of improving the adsorption performance of iodic acid ions.

In addition, the drying time may be such that the drying may be performed until the weight becomes constant. In most cases, the drying time is 8 hours or more, preferably 8 to 24 hours.

The granulated product obtained by drying can be used as it is as an adsorbent, or it may be lightly loosened and used. Further, the granulated product after drying may be crushed and used.

The iron (III) hydroxide obtained as described above is preferably further classified and then used as an adsorbent, particularly from the viewpoint of increasing the adsorption efficiency of iodic acid ions. For classification, for example, it is preferable to use a first sieve having a nominal opening of 1000 μm or less, particularly 600 μm or less, as defined in JISZ8801-1. It is also preferable to use a second sieve having a nominal opening of 212 μm or more, particularly 300 μm or more. Further, it is preferable to use these first and second sieves.

The adsorbent containing amorphous iron (III) hydroxide according to the present invention includes not only iodic acid ions, but also oxoacid ions and phosphorus containing heavy metals such as Cr, Mn, Mo, As, Sb and Se. It can also be used as an adsorbent for acid ions, fluorine ions and the like.

Further, the adsorbent containing amorphous iron (III) hydroxide according to the present invention is used as an adsorbent that simultaneously adsorbs iodic acid ion and iodide ion when used in combination with a poorly soluble silver compound. Can be done.

The poorly soluble silver compound has a solubility in 100 g of water at 20 ° C. of 10 mg or less, preferably 5 mg or less, but when the adsorbent of the present invention is subjected to water treatment such as passing liquid, the silver compound is used. It is preferable from the viewpoint that it can be prevented from melting and flowing out. Preferred examples of the poorly soluble silver compound include silver zeolite, silver phosphate, silver chloride, silver carbonate and the like.

The content of the poorly soluble silver compound in the adsorbent of the present invention is preferably 1% by mass or more as silver from the viewpoint of enhancing the adsorption performance of iodate ions and iodide ions, particularly iodide ions. The content of the poorly soluble silver compound is preferably 5% by mass or less as silver from the viewpoint of adsorbing iodic acid ions and iodide ions in a well-balanced manner.

The adsorbent containing amorphous iron (III) hydroxide and a poorly soluble silver compound may be, for example, a method of mixing iron (III) hydroxide and a poorly soluble silver compound in a dry or wet manner, or an amorphous one. It can be prepared by adding a sparingly soluble silver compound during the process of producing iron (III) hydroxide and extruding in the fourth step.

In the case of extrusion molding in the fourth step, extrusion molding may be difficult due to the addition of the sparingly soluble silver compound, but a lubricant or the like can be added if necessary.
Examples of the lubricant that can be used include talc, stearic acid, stearyl alcohol, zinc stearate, lead stearate, magnesium stearate, calcium stearate, stearic acid amide, oleic acid amide, erucic acid amide, and methylene bisstearic acid. Examples thereof include amide, ethylene bisstearic acid amide, stearic acid monoglyceride, stearyl stearate, hardened oil, liquid paraffin, paraffin wax, and synthetic polyethylene wax.
By adding the amount of the lubricating material to 1 to 20% by mass, preferably 2 to 10% by mass with respect to the amorphous iron (III) hydroxide, extrusion molding can be performed while maintaining sufficient adsorption performance. ..

Hereinafter, the present invention will be described with reference to Examples, but the present invention is not limited to these Examples.
<Evaluation device>
-X-ray diffractometer: Measured by a powder X-ray diffractometer Ultima IV manufactured by Rigaku. Cu-Kα was used as the radiation source. The measurement conditions were a tube voltage of 40 kV, a tube current of 40 mA, and a scanning speed of 2 ° / min.
-Thermal analysis (TG-DSC analysis): Using the thermogravimetric analyzer TGA / DSC1 manufactured by METTLER TOLEDO, a 10 mg sample was heated from 25 ° C. to 700 ° C. at a heating rate of 10 ° C./min in the atmosphere. The temperature of the exothermic peak appearing on the DSC temperature rise characteristic curve at that time was measured.
Further, the weight of the sample at 25 ° C. and the weight of the sample at 700 ° C. were measured, and the weight loss rate was calculated from the following formula.
Weight loss rate (%) = (AB) / A × 100
(A: Sample weight at 25 ° C, B: Sample weight at 700 ° C)
-Iodic acid ion concentration and iodide ion concentration in the iodic acid adsorption test: Measured by an ion chromatograph measuring device (ICS-1600 manufactured by DIONEX).
-BET specific surface area: Measured by Maxorb 1201 manufactured by Mountech.
-PH: Measured with a pH meter D-71 manufactured by HORIBA, Ltd.
-Electrical conductivity: Measured with an electric conductivity meter ES-51 manufactured by HORIBA, Ltd.

{Examples 1 to 4 and Comparative Examples 1 to 6}
<First process>
To 250 ml of a 20 wt% sodium hydroxide aqueous solution, 150 ml of an aqueous solution containing 39 wt% of iron (III) chloride was added over 40 minutes at room temperature (25 ° C.) (pH 8.8).
<Second process>
Then, the pH was adjusted to Table 1 with hydrochloric acid. Stirring was continued at 25 ° C. for 1 hour for aging.
<Third process>
Then, the aging slurry was repulped to the electrical conductivity shown in Table 1 and washed with water. The electric conductivity in Table 1 is the electric conductivity at 25 ° C. when the iron (III) hydroxide is made into a 10% by mass slurry.
<Fourth process>
Next, the iron (III) hydroxide slurry was dehydrated with a filter press and further squeezed to prepare iron (III) hydroxide having a water content shown in Table 1.
The water content was determined by drying 2.0 g of iron (III) hydroxide in a water-containing state at 110 ° C. and calculating the weight loss by drying as the water content.
Next, iron (III) hydroxide in a water-containing state with an adjusted water content was put into a wet extrusion granulator Multigran MG-55 manufactured by Dalton Co., Ltd., which was equipped with a screen having a perfect circle equivalent diameter of 0.6 mm at the tip and extruded. Molded. Next, the molded product extruded from the screen was dried at normal pressure for 12 hours at the temperature shown in Table 1 below.
In addition, the state of the extrusion molding machine during the molding process was visually observed to evaluate the granulation operability. The results are also shown in Table 1. The symbols in Table 1 indicate the following.
⊚; Extruded continuously. Extruded from most of the screen.
◯; Extruded continuously. Extruded from only part of the screen.
Δ: A small amount was extruded.
×; Almost not extruded.
Next, the obtained granulated product was lightly pulverized in an agate mortar, and the obtained pulverized product was sieved with an opening of 600 μm. At this time, the sieve was pulverized again, and all the pulverized products were passed through a sieve having an opening of 600 μm. The bottom of the sieve was collected and sieved with a mesh opening of 300 μm. This sieve was collected and used as a sample.
When the samples obtained in Examples 1 to 4, Comparative Examples 1 to 3 and Comparative Example 6 were subjected to X-ray diffraction analysis, no obvious diffraction peak was observed, and the sample was amorphous iron (III) hydroxide. It was confirmed.
The X-ray diffraction patterns of the samples obtained in Example 1 and Example 2 are shown in FIGS. 1 and 2.

<Physical property evaluation>
For the samples obtained in Examples, Comparative Examples 1 to 3 and Comparative Example 6, the exothermic peak temperature, the weight loss rate, the electric conductivity, and the BET specific surface area were measured. Further, the DSC temperature rise characteristic curves of the samples obtained in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 are shown in FIGS. 3, 4, 5 and 6, respectively.
As for the electric conductivity, the electric conductivity at 25 ° C. when the iron (III) hydroxide was made into a 10% by weight slurry in the third step was measured by an electric conductivity meter.

注）表中の「−」は未測定であることを示す。

Note) "-" in the table indicates that it has not been measured.

<Adsorption test 1>
Test 1;
Sodium iodate (NaIO ₃ ) was dissolved in ion-exchanged water as a reagent to prepare a test solution having an iodine-equivalent concentration of iodic acid of 200 ppm.
100 ml of this test solution and 0.10 g of the samples obtained in Examples, Comparative Examples 1 to 3 and Comparative Example 6 were placed in a 100 ml glass beaker and covered. After closing the lid, the mixture was stirred with a magnetic stirrer for 1 hour. After stirring, the test solution was filtered through a membrane filter having a pore size of 0.45 μm, and the iodine concentration was measured as the amount of iodic acid in the obtained filtrate. The adsorption rate of iodate ions was determined by dividing the difference in concentration before and after adsorption by the concentration before the adsorption test. The results are shown in Table 3. A similar test was also performed on a commercially available cerium hydroxide adsorbent, and the results are also shown in Table 3 as Comparative Example 7.

Exam 2;
The test seawater stock solution shown below was prepared, and the test seawater 1 containing 200 ppm of iodic acid was further prepared with the formulation shown below.
<Test seawater stock solution>
NaCl: 2.649%
MgCl ₂ : 0.326%
Sulfonyl ₄ : 0.207%
CaSO ₄ : 0.136%
KCl: 0.071%
<Test seawater 1>
Test seawater stock solution: 50.00 g
Ion-exchanged water: 949.69 g
NaIO ₃ : 0.31g
100 ml of this test solution and 0.10 g of the samples obtained in Examples, Comparative Examples 1 to 3 and Comparative Example 6 were placed in a 100 ml glass beaker and covered. After closing the lid, the mixture was stirred with a magnetic stirrer for 1 hour. After stirring, the test solution was filtered through a membrane filter having a pore size of 0.45 μm, and the iodine concentration was measured as the amount of iodic acid in the obtained filtrate. The adsorption rate of iodate ions was determined by dividing the difference in concentration before and after adsorption by the concentration before the adsorption test. The results are shown in Table 3.

注）表中の「−」は未測定であることを示す。

Note) "-" in the table indicates that it has not been measured.

Exam 3;
5 ml of the sample obtained in Example 2 was placed in a glass column (inner diameter 120 mm, length 450 mm) and washed with ion-exchanged water until the liquid became transparent. Next, 7695 g of ion-exchanged water and 0.46 g of NaIO ₃ were added to 405 g of the test seawater stock solution used in Test 2 to prepare test seawater 2 (8100 g) containing 50 ppm of iodic acid. This test seawater was passed through a column at 16.7 ml / min using Masterflex (manufactured by cole-parmer), and the test seawater after passing through the column was sampled and the iodic acid concentration was measured. From the measurement results obtained above, when the initial iodic acid concentration of the test seawater is Co and the iodic acid concentration after column passage is C, the numerical value represented by C / Co is shown on the vertical axis. FIG. 7 shows the total liquid flow capacity (VV) of the test seawater 2 with respect to 5 ml of the adsorbent sample on the horizontal axis.

{Examples 5 to 8}
After the completion of the first step of Example 2, a sparingly soluble silver compound was added to the amorphous iron (III) hydroxide in the amount shown in Table 3, and the mixture was sufficiently wet and mixed to form an amorphous iron (III) hydroxide. An adsorbent sample containing iron (III) hydroxide and a poorly soluble silver compound was prepared. The silver content in Table 4 indicates the amount of the poorly soluble silver compound added in terms of silver.

注）塩化銀（ＡｇＣｌ）は硝酸銀と塩化ナトリウムの反応により調製した。なお、塩化銀を含有する吸着剤サンプルを調製は、下記のように調製した。
硝酸銀５９．３ｇを１７８ｍＬのイオン交換水に溶解させた。塩化ナトリウム２０．４ｇを６１ｍＬのイオン交換水に溶解して硝酸銀溶液に添加し反応させた。反応により得られた塩化銀スラリーを第一工程終了後の非晶質の水酸化鉄（III）に添加した。
リン酸銀（Ａｇ_３ＰＯ_４）は硝酸銀とリン酸水素２ナトリウムの反応により調製した。なお、リン酸銀を含有する吸着剤サンプルを調製は、下記のように調製した。
リン酸水素２ナトリウム１２水塩３５．８ｇを３００ｍＬのイオン交換水に溶解した。硝酸銀５１．０ｇを１５０ｍＬのイオン交換水に溶解して、リン酸水素２ナトリウム水溶
液に添加し反応させた。反応により得られたリン酸銀スラリーを第一工程終了後の非晶質の水酸化鉄（III）に添加した。

Note) Silver chloride (AgCl) was prepared by the reaction of silver nitrate and sodium chloride. The adsorbent sample containing silver chloride was prepared as follows.
59.3 g of silver nitrate was dissolved in 178 mL of ion-exchanged water. 20.4 g of sodium chloride was dissolved in 61 mL of ion-exchanged water and added to a silver nitrate solution for reaction. The silver chloride slurry obtained by the reaction was added to amorphous iron (III) hydroxide after completion of the first step.
Silver phosphate (Ag ₃ PO ₄ ) was prepared by the reaction of silver nitrate and disodium hydrogen phosphate. The adsorbent sample containing silver phosphate was prepared as follows.
35.8 g of disodium hydrogen phosphate 12 hydroxide was dissolved in 300 mL of ion-exchanged water. 51.0 g of silver nitrate was dissolved in 150 mL of ion-exchanged water and added to a disodium hydrogen phosphate aqueous solution for reaction. The silver phosphate slurry obtained by the reaction was added to amorphous iron (III) hydroxide after completion of the first step.

<Adsorption test 2> Test 4;
By dissolving sodium chloride, calcium chloride, magnesium chloride, potassium iodide and iodic acid in ion-exchanged water, test seawater 3 having the following composition was prepared.
Test seawater 3
NaCl 0.132%
Ca ²⁺ 20ppm
Mg ²⁺ 63ppm
I ^- 200ppm
IO ₃ ^- 200ppm
100 ml of this test seawater 3 and 0.10 g of the sample obtained in any of Examples 2 and 5 to 8 were placed in a 100 ml glass beaker and covered. After closing the lid, the mixture was stirred with a magnetic stirrer for 1 hour. After stirring, the test solution was filtered through a pore size of 0.45μm membrane filter, iodide ion in the obtained filtrate (I ^{-) -} to determine the concentration of and iodate (IO _3). The difference in concentration before and after adsorption, by dividing the density before adsorption test, iodide ion was determined adsorption rate (I ^{- -)} and iodate (IO _3). These results are shown in Table 5.

As is clear from Table 5, the adsorbent containing amorphous iron (III) hydroxide and the poorly soluble silver compound produced in Examples 5 to 8 has a poorly soluble silver iodide ion adsorption rate. It can be seen that the improvement is improved as compared with the case where the compound is not added. Further, it can be seen that the balance between the amount of adsorption and removal of iodic acid ion and iodide ion can be adjusted by adjusting the amount of the sparingly soluble silver compound contained in the adsorbent.

Claims (5)

The first step of preparing a slurry containing iron (III) hydroxide by neutralizing an iron mineral salt and an alkali hydroxide in an aqueous solvent. The pH of the slurry is 70 ° C. or lower for 1 hour or longer. The second step of aging from 0 to 5.0, then the third step of washing with water until the electrical conductivity of the 10 mass% slurry containing iron (III) hydroxide becomes 14 mS / cm or less, and then after the washing treatment. A method for producing an adsorbent, which comprises a fourth step of extruding iron (III) hydroxide in a water-containing state and drying the obtained molded product at 150 ° C. or lower to obtain a granulated product. The method for producing an adsorbent according to claim 1, wherein the first step is to add a solution containing an iron mineral acid salt to an alkaline hydroxide aqueous solution to carry out a neutralization reaction. The method for producing an adsorbent according to claim 1 or 2, wherein the iron (III) hydroxide in the water-containing state of the fourth step is used having a water content of 40 to 60% by mass. The method for producing an adsorbent according to any one of claims 1 to 3, wherein the dried granulated product after the fourth step is crushed or pulverized. Any of claims 1 to 4, wherein a poorly soluble silver compound is added between the start of the first step of producing iron (III) hydroxide and the end of the third step, and extrusion molding is performed in the fourth step. The method for producing an adsorbent according to item 1.

Images