WO2018101286A1

WO2018101286A1 - Adsorbent containing amorphous iron (iii) hydroxide and method for manufacturing same

Info

Publication number: WO2018101286A1
Application number: PCT/JP2017/042708
Authority: WO
Inventors: 弘行桑野; 慎介宮部; 木ノ瀬　豊
Original assignee: 日本化学工業株式会社
Priority date: 2016-12-01
Filing date: 2017-11-29
Publication date: 2018-06-07
Also published as: JP6779768B2; JP2018089570A

Abstract

Provided are: an adsorbent, containing iron (III) hydroxide, that can also be used upon being packed into a column, etc., and that has an excellent performance of adsorbing iodate ions in particular; and an industrially advantageous method for manufacturing the adsorbent. This adsorbent is characterized in containing an amorphous iron (III) hydroxide in which the temperature of a heat generation peak occurring on a DSC temperature rise characteristics curve for a 25-700°C temperature rise is 350-400°C, the weight decrease ratio when the temperature is raised from 25°C to 700°C is 18% or above, and the electrical conductivity is 14 mS/cm or below. The adsorbent preferably has a BET specific surface area of 100-300 m²/g and is more preferably a granulated product.

Description

Adsorbent containing amorphous iron (III) hydroxide and method for producing the same

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

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

As a method for removing these radioactive iodines, the following method is used.
(1) A method of collecting iodine-containing gas or liquid as silver iodide by bringing it into contact with silver zeolite.
(2) A method of collecting radioactive iodine (iodine 131) by isotopic exchange with non-radioactive iodine using a large amount of impregnated activated carbon impregnated with potassium iodide.
(3) A method of removing iodine-containing gas or liquid by contacting with an ion-exchangeable fiber having an amino group.
(4) A method of 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 using iron (III) hydroxide as an adsorbent has also been proposed.
Non-Patent Document 1 proposes to coprecipitate and remove iodate ions in iron (III) hydroxide produced by adding iron nitrate (III) and sodium hydroxide to a solution containing iodate ions. ing.
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 hydroxide (III) is used as an adsorbent. Proposed.

JP 2016-123902 A

Recently, in addition to iodine, hydroiodic acid, and methyl iodide, removal of iodate (IO ₃ ) ions has become a problem. This is because sodium hypochlorite is used in the treatment process of the primary contaminated water, so iodine ions in the contaminated water are oxidized by sodium hypochlorite to generate iodate ions. Estimated.

Inorganic adsorbents such as silver zeolite and cerium hydroxide are excellent in adsorption performance of iodate ions, but are expensive and not industrially advantageous.

Iron (III) hydroxide is an inexpensive material, but further improvement in adsorption performance for iodate ions and the like is required.

For example, radioactive materials discharged from nuclear facilities are removed by adsorption by a water treatment system having a column (adsorption tower) filled with a radioactive material adsorbent.

In Non-Patent Document 1 relating to a conventional iron hydroxide (III) adsorbent, iodic acid is used for coprecipitation and removal of iron (III) hydroxide produced from a solution containing iodate ions. The conditions on the solution side containing ions have been studied, but no study has been made on the adsorbent technology used by collecting the iron (III) hydroxide from the reaction solution and filling it in a column or the like.

In addition, the adsorbent used for packing in a column or the like is usually a granulated product. However, an adsorbent obtained by granulating iron (III) hydroxide using a binder is used for removing iodate ions. Then, the adsorption | suction performance with respect to an iodate ion tends to fall with a binder component. In addition, the adsorbent in which iron (III) hydroxide is supported on other inorganic materials and organic materials has a problem that the adsorption performance is low because the content of iron hydroxide (III) as an active ingredient is low. is there.

Therefore, the object of the present invention can be used even when packed in a column or the like, and particularly an adsorbent containing iron (III) hydroxide having excellent iodate ion adsorption performance and an industrially advantageous production method thereof Is to provide.

As a result of intensive studies in view of the above circumstances, the present inventors have found that the temperature of the exothermic peak appearing on the DSC temperature rise characteristic curve in the temperature rise process at 25 to 700 ° C. is in a specific range, and the temperature rises to 25 to 700 ° C. In particular, by obtaining amorphous iron hydroxide (III) having a weight reduction rate of not less than a specific value and an electric conductivity of not more than a specific range, it is particularly excellent in adsorption performance of iodate ions, and a binder. It becomes amorphous iron hydroxide (III) that can be granulated without using. Furthermore, even when the amorphous iron (III) hydroxide is used as a granulated product, it has been found that it has particularly excellent iodate ion adsorption performance, and the present invention has been completed.

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

The adsorbent production method to be provided by the present invention is a method for preparing a slurry containing iron (III) hydroxide by carrying out a neutralization reaction between an iron mineral acid salt and an alkali hydroxide in an aqueous solvent. One step, a second step of aging the slurry at pH 3.0 to 5.0, and then washing with water until the electric conductivity of a 10% by weight slurry containing iron (III) hydroxide is 14 mS / cm or less And a fourth step of extruding the water-containing iron hydroxide (III) after the washing treatment and drying the resulting 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 when packed in a column or the like, and particularly has excellent iodate ion adsorption performance. Amorphous iron hydroxide (III) effective as the adsorbent can be produced by an industrially advantageous method.

2 is an X-ray diffraction pattern of amorphous iron (III) hydroxide obtained in Example 1. FIG. 3 is an X-ray diffraction pattern of amorphous iron (III) hydroxide obtained in Example 2. FIG. 2 is a DSC temperature rise characteristic curve of amorphous iron (III) hydroxide obtained in Example 1. 2 is a DSC temperature rise characteristic curve of amorphous iron (III) hydroxide obtained in Example 2. 2 is a DSC temperature rise characteristic curve of amorphous iron (III) hydroxide obtained in Comparative Example 1. 2 is a DSC temperature rise characteristic curve of amorphous iron (III) hydroxide obtained in Comparative Example 2. The figure which shows the result of the column test which uses the amorphous iron hydroxide (III) obtained in Example 2 as an adsorbent.

Hereinafter, the present invention will be described based on preferred embodiments 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, granulated particles obtained by granulating the powder, or a mixture thereof. Also good.
The powder used herein preferably has a median diameter D50 of 1 to 100 μm according to a laser diffraction / scattering particle size distribution method.

The amorphous iron hydroxide (III) used as the adsorbent in the present invention is preferably a granulated product from the viewpoint of being used after being packed in a column. The particle size of the granulated product is preferably 200 to 1000 μm, more preferably 300 to 600 μm. Specifically, when a sieve having an aperture of 212 μm and a sieve of 1 mm according to JIS Z8801-1 standard is used, 98% by mass or more, particularly 99% by mass or more of the adsorbent passes through the sieve having an aperture of 1 mm, and It is preferable that 98% by mass or more, particularly 99% by mass or more, does not pass through a sieve having an aperture 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 into the adsorption tower and pass the water because the powder hardly clogs in the adsorption tower. In addition, it is preferable that the adsorbent of the present invention has a small particle size of more than 1 mm because the adsorbent has a high adsorbing ability and can improve the entire adsorbing performance. In particular, when a 300 μm sieve and a 600 μm sieve according to JIS Z8801-1 standard are used, 98% by mass or more, particularly 99% by mass or more of the adsorbent passes through the 600 μm sieve and 98% by mass. In particular, 99% by mass or more preferably does not pass through a sieve having an opening of 300 μm.

As the amorphous iron hydroxide (III) 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 temperature rising process at 25 to 700 ° C. is used. There is one of the features.

In the amorphous iron hydroxide (III) used in the adsorbent of the present invention, the reason why the temperature of the exothermic peak is in the above range is that the adsorption performance of iodate ions is particularly low when the exothermic peak temperature is outside the above range. This is because the granulation process becomes difficult. Further, the amorphous iron hydroxide (III) used in the adsorbent of the present invention preferably has an exothermic peak of 370 to 400 ° C. from the viewpoint of further improving the adsorption performance of iodate ions, A temperature of 370 to 390 ° C. is particularly preferable.

It is one of the characteristics that amorphous iron hydroxide (III) used in the adsorbent of the present invention has a weight reduction rate of 18% or more when the temperature is raised to 25 to 700 ° C.

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

One feature of the amorphous iron hydroxide (III) used in the adsorbent of the present invention is that it has an electrical conductivity of 14 mS / cm or less in addition to the above physical properties.

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

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

In addition to the above physical properties, the amorphous iron hydroxide (III) used in the adsorbent of the present invention has 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 iodate ions.

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

Hereinafter, the manufacturing method of the 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 in the first step include iron (III) chloride, iron (III) sulfate, and iron (III) nitrate.
The iron mineral acid salt is used as an aqueous solution in which 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, and aqueous ammonia.
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 iron mineral acid salt may be brought into contact with each other. For example, (1) a method in which an aqueous solution containing an iron mineral acid salt is added to an aqueous alkali hydroxide solution to carry out a neutralization reaction, and (2) an aqueous solution containing an iron mineral acid salt is neutralized by adding an aqueous alkali hydroxide solution Examples include a method of performing a reaction, and (3) a method of performing a neutralization reaction by simultaneously adding an aqueous solution containing an alkali hydroxide aqueous solution and an iron mineral acid salt into an aqueous solvent.
In this production method, the contact method of the aqueous alkali hydroxide solution and the aqueous solution containing iron mineral acid salt is performed by the method (1) above from the viewpoint of obtaining a product with good yield and good adsorption performance. preferable.

Addition of an aqueous solution containing an iron mineral acid salt and / or an aqueous alkali hydroxide solution, when the reaction temperature is high, crystallization of iron (III) hydroxide may proceed and the adsorption performance may be lowered. It is preferably carried out at 70 ° C. or less, more preferably 10 to 70 ° C. *

The addition rate of the aqueous solution containing the iron mineral acid salt or the aqueous alkali hydroxide solution is not particularly limited, but when added to the other solution so as to be a constant rate, a stable quality can be obtained. It is preferable from the viewpoint.

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

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

In the method for producing the present adsorbent, by performing this second step, it is particularly excellent in the adsorption performance of iodate ions, and it can be agglomerated by a synergistic effect with the washing treatment in the third step described later. Quality iron (III) hydroxide can be produced.

In the second step, it is important that the pH of the slurry containing iron (III) hydroxide obtained in the first step is adjusted to 3.0 to 5.0 and ripened. This is because, in the second step, when the pH of the slurry containing iron (III) hydroxide is outside the above range, the adsorption performance of iodate ions is particularly inferior and the granulation treatment becomes difficult. In the present invention, the second step is a slurry containing iron (III) hydroxide, particularly from the viewpoint of obtaining amorphous iron hydroxide (III) that is excellent in iodate ion adsorption performance 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 in the second step is preferably 90 ° C. or less, preferably 70 ° C. or less, more preferably 10 to 70 ° C. from the viewpoint of preventing crystallization of iron (III) hydroxide. The aging time for the second step is 1 hour or more, preferably 1 to 12 hours.

The slurry containing iron hydroxide (III) subjected to the aging treatment in the second step is subjected to a washing treatment in the third step.

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

In this adsorbent production method, ionic impurities such as halogen ions, sulfate ions, nitrate ions, ammonium ions and alkali metal ions are removed from iron (III) hydroxide in this third step in addition to the second step described above. As a result, amorphous iron hydroxide (III) that can be granulated while maintaining excellent adsorption performance of iron hydroxide (III) can be obtained.

There is no particular limitation on the method for washing iron hydroxide (III) in the third step, but it is particularly preferable to carry out by means such as repulping.

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

In the fourth step, water-containing iron hydroxide (III) subjected to the washing treatment after the third step is extruded to obtain a molded product, and the molded product is dried to obtain amorphous iron hydroxide (III ).

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

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

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

As the shape of the hole formed in the opening member, a circle, a triangle, a polygon, an annulus, and the like can be given. The true circle equivalent diameter of the opening 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 true circle equivalent diameter here is a diameter of a circle calculated from the area when the area of one hole is a 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 iodate ions and the like.
In the present production method, the reason for setting the drying temperature of the molded product in the above range is that when the drying temperature of the molded product exceeds 150 ° C., the reduction of surface hydroxyl groups contributing to adsorption becomes significant, and sufficient adsorption performance is not exhibited. It is. In this production method, the drying temperature of the molded article is preferably 80 to 150 ° C., more preferably 80 to 120 ° C., particularly from the viewpoint of improving the adsorption performance of iodate ions.

Further, the drying time may be performed until the weight becomes constant. In many cases, the drying time is 8 hours or more, preferably 8 to 24 hours.

The granulated product obtained by drying can be used as an adsorbent as it is, or it can be used after lightly loosening. The granulated product after drying may be used after being pulverized.

The iron hydroxide (III) obtained as described above is preferably further classified and then used as an adsorbent, particularly from the viewpoint of increasing the adsorption efficiency of iodate ions. For the classification, for example, it is preferable to use a first sieve having a nominal opening prescribed in JISZ8801-1 of 1000 μm or less, particularly 600 μm or less. Moreover, it is also preferable to perform using the 2nd sieve whose said nominal opening is 212 micrometers or more, especially 300 micrometers or more. Furthermore, it is preferable to carry out using these first and second sieves.

The adsorbent containing amorphous iron (III) hydroxide according to the present invention includes iodate ions, oxo acid ions containing heavy metals such as Cr, Mn, Mo, As, Sb, and Se, phosphorus It can also be used as an adsorbent for acid ions, fluorine ions and the like.

Furthermore, the adsorbent containing amorphous iron hydroxide (III) according to the present invention is used as an adsorbent that simultaneously adsorbs iodate ions and iodide ions when used in combination with a poorly soluble silver compound. I can do it.

The hardly soluble silver compound has a solubility in 100 g of water at 20 ° C. of 10 mg or less, preferably 5 mg or less. When the adsorbent of the present invention is subjected to water treatment such as liquid flow, the silver compound is It is preferable from the viewpoint that dissolution and outflow can be prevented. Preferable examples of the hardly soluble silver compound include silver zeolite, silver phosphate, silver chloride, and silver carbonate.

In the adsorbent of the present invention, the content of the hardly soluble silver compound 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. Further, the content of the hardly soluble silver compound is preferably 5% by mass or less as silver from the viewpoint of adsorbing iodate ions and iodide ions in a balanced manner.

The adsorbent containing amorphous iron hydroxide (III) and a hardly soluble silver compound can be prepared by, for example, a method of mixing iron (III) hydroxide and a hardly soluble silver compound in a dry or wet manner, It can be prepared by using a method in which a hardly soluble silver compound is added during the step of producing iron (III) hydroxide and extrusion is performed in the fourth step.

When extrusion molding is performed in the fourth step, the extrusion molding may be difficult due to the addition of the hardly soluble silver compound, but a lubricant or the like can be added if necessary.
Examples of lubricants 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 methylenebisstearic acid. Examples thereof include amides, ethylenebisstearic acid amides, stearic acid monoglycerides, stearyl stearate, hydrogenated oils, liquid paraffin, paraffin wax, and synthetic polyethylene wax.
By adding 1 to 20% by mass, preferably 2 to 10% by mass, the amount of lubricant added to amorphous iron hydroxide (III), extrusion molding can be performed while maintaining sufficient adsorption performance. .

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.
<Evaluation equipment>
X-ray diffractometer: Measured with a powder X-ray diffractometer Ultima IV manufactured by Rigaku Corporation. 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 a thermogravimetric measuring device TGA / DSC1 manufactured by METTLER TOLEDO, a 10 mg sample was heated from 25 ° C. to 700 ° C. in the air at a heating rate of 10 ° C./min. The temperature of the exothermic peak appearing on the DSC temperature rise characteristic curve 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 reduction rate was calculated from the following formula.
Weight reduction rate (%) = (AB) / A × 100
(A: sample weight at 25 ° C., B: sample weight at 700 ° C.)
-Iodate ion concentration and iodide ion concentration in iodic acid adsorption test: Measured with an ion chromatograph measuring device (ICS-1600 manufactured by DIONEX).
-BET specific surface area: Measured with a Macsorb 1201 manufactured by Mountaintech.
PH: Measured with a pH meter D-71 manufactured by HORIBA, Ltd.
Electrical conductivity: Measured with an electrical conductivity meter ES-51 manufactured by Horiba, Ltd.

{Examples 1 to 4 and Comparative Examples 1 to 6}
<First step>
To 250 ml of 20 wt% sodium hydroxide aqueous solution, 150 ml of an aqueous solution containing 39 wt% of iron (III) chloride was added at room temperature (25 ° C.) over 40 minutes (pH 8.8).
<Second step>
Subsequently, it adjusted so that pH might become Table 1 with hydrochloric acid. Stirring was continued for 1 hour at 25 ° C., followed by aging.
<Third step>
Next, the aged slurry was repulped until the electrical conductivity shown in Table 1 was reached, and washed with water. In addition, the electrical conductivity of Table 1 is the electrical conductivity at 25 ° C. when the iron hydroxide (III) 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 water-containing iron hydroxide (III) 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 loss on drying as the water content.
Next, iron hydroxide (III) in a water-containing state with adjusted water content was put into a Dalton wet extrusion granulator Multigran MG-55 equipped with a screen with a diameter of 0.6 mm at the tip, and extruded. Molded. Next, the molded product extruded from the screen was subjected to drying treatment at normal pressure for 12 hours at the temperature described in Table 1 below.
Moreover, the state of the extrusion molding device during the molding process was visually observed to evaluate the granulation operability. The results are also shown in Table 1. In addition, the symbol in Table 1 shows the following.
A: Extruded continuously. Extruded from most of the screen.
○: Extruded continuously. Extruded from only a part of the screen.
Δ: A small amount was extruded.
X: Almost not extruded.
Subsequently, the obtained granulated product was lightly pulverized in an agate mortar, and the obtained pulverized product was passed through a sieve having an opening of 600 μm. At this time, the sieve was pulverized again, and all the pulverized material was passed through a sieve having an opening of 600 μm. The sieve was collected and passed through a sieve having an opening of 300 μm. The sieve top 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 clear 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.

<Physical property evaluation>
The samples obtained in Examples, Comparative Examples 1 to 3 and Comparative Example 6 were measured for exothermic peak temperature, weight loss rate, electrical conductivity, and BET specific surface area. Further, 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.
In addition, electric conductivity measured the electric conductivity in 25 degreeC when this iron (III) hydroxide was made into 10 weight% slurry in the 3rd process with the electric conductivity meter.

Note) “-” in the table indicates unmeasured.

<Adsorption test 1>
Test 1;
Sodium iodate (NaIO ₃ ) as a reagent was dissolved in ion-exchanged water 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 capped. After capping, 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. Further, a similar test was performed on a commercially available cerium hydroxide adsorbent, and the results are also shown in Table 3 as Comparative Example 7.

Test 2;
The test seawater stock solution shown below was prepared, and test seawater 1 containing 200 ppm of iodic acid with the following formulation was prepared.
<Test seawater stock solution>
NaCl: 2.649%
MgCl ₂ : 0.326%
MgSO ₄ : 0.207%
CaSO _4: 0.136%
KCl: 0.071%
<Test seawater 1>
Seawater stock solution for testing: 50.00g
Ion exchange water: 949.69g
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 capped. After capping, 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.

Note) “-” in the table indicates unmeasured.

Test 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 water through ion exchange 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 the column at 16.7 ml / min using Master Flex (manufactured by cole-parmer), the test seawater after passing through the column was sampled, and the iodic acid concentration was measured. From the measurement results obtained above, the vertical axis indicates the numerical value represented by C / Co, where Co is the initial iodic acid concentration of the test seawater and C is the concentration of iodic acid after passing through the column, FIG. 7 shows the total liquid passing volume (BV) 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, the hardly soluble silver compound was added to amorphous iron hydroxide (III) in the addition amount shown in Table 3, and mixed well by wet to form amorphous An adsorbent sample containing iron (III) hydroxide and a hardly soluble silver compound was prepared. In addition, silver content in Table 4 shows the addition amount which converted the hardly soluble silver compound into silver.

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 exchange water. 20.4 g of sodium chloride was dissolved in 61 mL of ion exchange water and added to the silver nitrate solution to react. 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.
Dissolve 35.8 g of disodium hydrogen phosphate 12 hydrate in 300 mL of ion exchange water. 51.0 g of silver nitrate was dissolved in 150 mL of ion exchange water and added to a disodium hydrogen phosphate aqueous solution to react. 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;
Test seawater 3 having the following composition was prepared by dissolving sodium chloride, calcium chloride, magnesium chloride, potassium iodide, and iodic acid in ion-exchanged water.
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 Example 2 and Examples 5 to 8 were placed in a 100 ml glass beaker and capped. After capping, 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 concentrations of iodide ion (I ⁻ ) and iodate ion (IO ₃ ⁻ ) in the obtained filtrate were measured. The adsorption rate of iodide ion (I ⁻ ) and iodate ion (IO ₃ ⁻ ) was determined by dividing the difference in concentration before and after the adsorption by the concentration before the adsorption test. These results are shown in Table 5.

As is apparent from Table 5, the adsorbent prepared in Examples 5 to 8 containing amorphous iron (III) hydroxide and a poorly soluble silver compound has a poorly soluble silver ion adsorption rate. It turns out that it improves compared with the thing which does not add a compound. Moreover, it turns out that the balance of the adsorption removal amount of an iodate ion and iodide ion can be adjusted by adjusting the addition amount of the poorly soluble silver compound contained in adsorption agent.

Claims

The temperature of the exothermic peak appearing on the DSC temperature rise characteristic curve in the temperature rise process at 25 to 700 ° C. is 350 to 400 ° C., the weight loss rate when the temperature rises to 25 to 700 ° C. is 18% or more, and An adsorbent comprising amorphous iron (III) hydroxide having a degree of 14 mS / cm or less.
The adsorbent according to claim 1, wherein the BET specific surface area is 100 to 300 m 2 / g.
The adsorbent according to claim 1, wherein the adsorbent is a granulated product.
The adsorbent according to claim 3, wherein the granulated product has a particle size of 200 to 1000 µm.
The adsorbent according to any one of claims 1 to 4, wherein the adsorbing substance is iodate ion.
The adsorbent according to any one of claims 1 to 5, further comprising a hardly soluble silver compound.
The adsorbent according to claim 6, wherein the adsorbing substances are iodate ions and iodide ions.
A first step of preparing a slurry containing iron (III) hydroxide by neutralizing an iron mineral acid salt and an alkali hydroxide in an aqueous solvent, and aging the slurry at a pH of 3.0 to 5.0 The second step, then the third step of washing with water until the electric conductivity of the 10% by mass slurry containing iron (III) is 14 mS / cm or less, then the water-containing iron hydroxide after the washing treatment ( A fourth step of extruding III) and drying the resulting molded product at 150 ° C. or lower to obtain a granulated product, and a method for producing an adsorbent.
The method for producing an adsorbent according to claim 8, wherein the first step performs a neutralization reaction by adding a solution containing an iron mineral acid salt to an alkali hydroxide aqueous solution.
10. The production of the adsorbent according to claim 8, wherein the water-containing iron hydroxide (III) used in the fourth step has a water content of 40 to 60% by mass. Method.
The method for producing an adsorbent according to any one of claims 8 to 10, wherein the dried granulated product after the fourth step is crushed or pulverized.