日本原子力研究開発機構機関リポジトリ
Japan Atomic Energy Agency Institutional Repository

Title

Removalofcesiumusing

cobalt-ferrocyanide-impregnatedpolymer-chain-grafted fibers

Ryo ISHIHARA, Kunio FUJIWARA, Takato HARAYAMA, Yusuke
OKAMURA, Shoichiro UCHIYAMA, Mai SUGIYAMA, Taka-aki
Author(s)SOMEYA, Wataru AMAKAI, Satoshi UMINO, Tsubasa ONO, Aguru
NIDE, Yuya HIRAYAMA, Tsukasa BABA, Takashi KOJIMA, Daisuke
UMENO, Kyoichi SAITO ,* Shiho ASAI and Takanobu SUGO

Citation
Text Version
URL
DOI

Journal of Nuclear Science and Technology, 48(10) ;p.1281-1284
Authorhttp://jolissrch-inter.tokai-sc.jaea.go.jp/search/servlet/search?5030946
http://dx.doi.org/10.3327/jnst.48.1281

This is an Author's Accepted Manuscript of an article published in[include the complete citation information for the final version of
Right

the article as published in] the Journal of Nuclear Science andTechnology, 2011 ©Taylor & Francis, available online at:
http://www.tandfonline.com/

Japan Atomic Energy Agency

RAPID COMMUNICATION

Removal of Cesium Using Cobalt-Ferrocyanide-Impregnated
Polymer-Chain-Grafted Fibers
Ryo ISHIHARA1, Kunio FUJIWARA1,2, Takato HARAYAMA1, Yusuke OKAMURA1,
Shoichiro UCHIYAMA1, Mai SUGIYAMA1, Taka-aki SOMEYA1, Wataru AMAKAI1,
Satoshi UMINO1, Tsubasa ONO1, Aguru NIDE1, Yuya HIRAYAMA1, Tsukasa BABA1,
Takashi KOJIMA1, Daisuke UMENO1, Kyoichi SAITO1 , * Shiho ASAI3 andTakanobu SUGO2
1

Department of Applied Chemistry and Biotechnology, Chiba University, Inage-ku, Chiba
264-8522, Japan

2

Environment Purification Institute Co., Shinden-machi, Takasaki, Gunma 370-0833, Japan

3

Nuclear Science and Engineering Directorate, Japan Atomic Energy Agency, Tokai-mura,Naka-gun, Ibaraki 319-1195, Japan(Received)

KEYWORDS: radiation-induced graft polymerization, cesium ion removal, cobalt
ferrocyanides, 6-nylon fiber, adsorbent

I. Introduction
Radioisotopes are currently being released by Fukushima Daiichi nuclear power plant,
which was damaged by the magnitude-9.0 earthquake and the tsunami that followed.
Cesium-137, cesium-134, and iodine-131 produced by the fission of nuclear fuels are
expected to seriously contaminate the sea and ground.

Cesium and iodine dissolve in waterand seawater in ionic forms of Cs+ and I- or IO3-, respectively.

Cesium-137, with a longer

half-life (30 years) than iodine-131 (8 days), should be removed and confined.
*

Corresponding author, E-mail: marukyo@faculty.chiba-u.jp1

Adsorption is a feasible method of removing radioactive species from watercontaminated with radioisotopes. Zeolites and insoluble metal ferrocyanides1) are known as
adsorbents capable of specifically capturing cesium-137 ions.

Moreover, the insoluble metal

ferrocyanides are loaded onto solid supports in bead or granule form such as porousanion-exchange resins2-4), silica gels5,6), and zeolites7).

However, fibrous adsorbents are

effective for easy operation at sites for processing water contaminated with radioisotopes.
Here, we propose a novel fiber that can immobilize metal ferrocyanides for theremoval of cesium ions using a commercially available 6-nylon fiber as a starting material.
Precipitates of metal ferrocyanide (M-FC) were formed among the polymer chains grafted
onto the 6-nylon fiber.

Therefore, the M-FC-impregnated fibers with a small diameter

enhance the mass transfer of cesium ions from the bulk of liquid to the M-FC particles,
leading to the rapid removal of cesium ions.

In addition, the M-FC-impregnated fibers canbe fabricated into various fiber modules for easy operation at the sites. In this study, thecobalt ion was used as a metal ion that precipitates with potassium ferrocyanide.

II. Experimental
1. Materials
6-Nylon fiber of 40 μm diameter, which was purchased from Toray Co., was used as thetrunk polymer for grafting.

Vinyl benzyl trimethylammonium chloride (VBTAC,

CH2=CHC6H4CH2N(CH3)3Cl) was supplied by AGC Seimi Chemical Co. Sodium styrene
sulfonate (SSS, CH2=CHC6H4SO3Na) was purchased from Wako. VBTAC and SSS wereused without further purification. Potassium hexacyanoferrate(II) trihydrate and cobalt(II)chloride hexahydrate were purchased from Wako.
grade or higher.
mg-Cs/L.

The other chemicals were of analytical

Cesium chloride was dissolved with seawater to yield a concentration of 10

Seawater obtained offshore of Odawara in Kanagawa Prefecture, Japan was

supplied by the Research Institute of Salt and Sea Water Science.

2. Impregnation of Cobalt Ferrocyanide onto VBTAC- and SSS-Fibers
Two impregnation schemes of cobalt ferrocyanide onto VBTAC- and SSS-grafted
6-nylon fibers are shown in Figs. 1 (a) and (b), respectively.
2

Each scheme consists of four

steps.

(1) Electron-beam irradiation8,9): Nylon fiber or 6-nylon fiber was irradiated with anelectron beam in nitrogen atmosphere at ambient temperature.

The dose was 200 kGy. (2)VBTAC or SSS grafting: The irradiated Nylon fiber was immersed in 0.5 M VBTAC or 0.5
M SSS aqueous solution for a prescribed reaction time at 313 K.

The degree of VBTAC or

SSS grafting was evaluated from the mass gain of the fiber as

Degree of VBTAC or SSS grafting (%) = 100 (W1 – W0)/W0(1)

where W0 and W1 are the masses of the trunk and VBTAC- or SSS-grafted fibers, respectively.
The resulting VBTAC- and SSS-grafted fibers are hereafter referred to as the VBTAC and
SSS fiber, respectively. From the viewpoint of the physical strength of the VBTAC and SSS
fibers, dgs were set at 25 and 73%, respectively. (3-a) Binding of ferrocyanide ions to thetrimethylammonium group of the VBTAC fiber: The VBTAC fiber was immersed in 0.1 M
potassium ferrocyanide aqueous solution at 298 K for 30 min. (3-b) Binding of cobalt ionsto the sulfonic group of the SSS fiber: The SSS fiber was immersed in 0.11 M CoCl2
aqueous solution at 298 K for 1 h.

(4-a) Precipitation of cobalt ferrocyanide onto the

VBTAC fiber: The ferrocyanide-ion-bound fiber was reacted with 0.11 M CoCl2 aqueous
solution at 298 K for 3 h to precipitate cobalt ferrocyanide (Co-FC). (4-b) Precipitation ofcobalt ferrocyanide onto the SSS-fiber: The cobalt-ion-bound fiber was reacted with 0.11 M
potassium ferrocyanide aqueous solution at 298 K for 1 h to precipitate Co-FC.
After the fibers were immersed in a 1.0 M NaCl aqueous solution and washedrepeatedly with water, they were vacuum-dried.

The resultant Co-FC-impregnated fibers

prepared via VBTAC and SSS grafting onto the nylon fibers are hereafter referred to as the
VBTAC- and SSS-Co-FC fibers, respectively.

The content of Co-FC impregnated wasevaluated from the mass gain of the fiber asContent of Co-FC impregnated (%) = 100 (W2 – W1)/W2(2)

where W2 is the mass of the VBTAC- or SSS-Co-FC fiber.
The crystalline phases of the VBTAC- and SSS-Co-FC fibers were identified by X-ray
diffractometry (XRD, Bruker, D8 Advance) using CuKα radiation. The distributions of3

ferrocyanide and cobalt ions inside the ferrocyanide-ion-bound VBTAC and VBTAC-Co-FC
fibers were determined by scanning electron microscopy/energy-dispersive X-ray
spectroscopy system (SEM/EDS. JEOL, JSM-6510A).

3. Cesium Adsorption in Batch Mode Using VBTAC- and SSS-Co-FC Fibers
As a preliminary experiment, the cesium adsorption experiment using 10 mg-Cs/L
cesium chloride dissolved with a 0.5 M NaCl aqueous solution was performed to confirm
high selectivities of the VBTAC- and SSS-Co-FC fibers.

Approximately 0.2 g of the

VBTAC- or SSS-Co-FC fiber was immersed in 20 mL of 10 mg-Cs/L cesium solution. Aftergentle stirring at 298 K for a prescribed contact time, the supernatant was sampled and thecesium concentration in seawater was determined by ICP-MS.
from 3 to 60 min.

The contact time ranged

The removal percentage (R) of cesium from the solution and the

distribution coefficient (Kd) were evaluated as

Removal percentage (%) = 100 (Ci – Ct)/Ci(3)

Distribution coefficient (cm3/g) = [(Ci – Cf) V/W]/Cf(4)

where Ci and Cf are the initial and final cesium concentrations, respectively, and Ct is thecesium concentration after the prescribed contact time.

V and W are the volume of thesolution and weight of the VBTAC- or SSS-Co-FC fiber, respectively.

III. Results and Discussion
The contents of VBTAC- and SSS-Co-FC impregnated were 5.1 and 7.3%,
respectively, which were lower than that (21%) of nickel-ferrocyanide impregnated onto
zeolite7).

The diameter of the Nylon fiber (40 μm) in the dry state increased to the diametersof the VBTAC (45 μm) and SSS (56 μm) fibers in the dry state. The XRD patterns of
6-nylon, VBTAC-, and SSS-Co-FC fibers are shown in Fig. 2.

Although apparent

diffraction peak of Co-FC was not observed on the diffraction pattern of the VBTAC-Co-FC
fiber (Fig. 2(b)), the formation of K2Co[Fe(CN)6] (ICDD Card No. 00-031-1000) was
confirmed on the SSS-Co-FC fiber (Fig. 2(c)).
4The distribution of iron across the ferrocyanide-ion-bound VBTAC fiber is shown in
Fig. 3 (a). The distributions of iron and cobalt across the VBTAC-Co-FC fiber measured
using EDS are shown in Figs. 3 (b) and (c), respectively. The uniform Fe or ferrocyanide
distribution across the ferrocyanide-ion-bound VBTAC fiber corresponds to the uniform
distribution of the poly-VBTAC chain grafted to the Nylon fiber.

On the other hand, Fe andCo were observed only in the periphery of the VBTAC-Co-FC fiber, which was treated with
1.0 M NaCl.
The adsorption rates of cesium ions in seawater onto the VBTAC- and SSS-Co-FC
fibers were evaluated in batch mode.

As shown in Table 1, after immersing the fibers inseawater for 30 min, the cesium concentrations became lower than the detection limits of
ICP-MS (0.2 mg-Cs/L).

This is indicative of the rapid mass transfer of cesium ions to the

Co-FC impregnated onto the fibers. From the results of Fig. 3 and Table 1, Co-FC phase
was evidently formed on the VBTAC-Co-FC fiber.

The Co-FC phase with small size andlow crystallinity will be formed on the periphery of the VBTAC-Co-FC fiber. The recovery
percentages of the VBTAC– and SSS-Co-FC fibers in seawater were higher than 98% and the
distribution coefficients were at least 4.9 × 103. The VBTAC– or SSS-Co-FC fiber as anadsorbent for the removal of cesium ions should be selected on the basis of the production
cost and mechanical strength of the fiber.
The mass-transfer characteristics of the fibers are advantageous because the fibers canbe regarded as a strand of small beads10). Moreover, the flow resistance of the fiber module
is adjustable simply by controlling the packing density of the fibers.

The

Co-FC-impregnated fibers prepared in this study are promising for the rapid removal ofcesium ions from cesium-ion-containing solutions by an easy operation.

IV. Conclusion
Sparingly soluble metal ferrocyanide (M-FC) salts are formed in liquid by mixing a
metal salt solution with potassium ferrocyanide solution.

Therefore, for use as an adsorbent,

M-FCs have thus far been impregnated onto various solid supports such as porous
ion-exchange beads, silica gel, and activated carbon.

To achieve the rapid capture of cesium

ions and easy processing of highly radioactive water, we prepared a novel M-FC-impregnatedfiber by radiation-induced graft polymerization and subsequent chemical modifications.
5Ferrocyanide and cobalt ions were bound to vinyl benzyl trimethylammmonium chloride- andsodium styrene sulfonate-grafted 6-nylon fibers, respectively, via an ion-exchange interaction.
Subsequently, the bound ferrocyanide and cobalt ions were reacted with cobalt and potassium
ferrocyanide ions, respectively, to form insoluble or sparingly soluble cobalt-ferrocyanide(Co-FC).

The resultant Co-FC-impregnated fibers exhibited a high affinity to cesium ions inseawater. Such fibers can be fabricated into various fiber modules suitable for the removalof radioisotopes at sites.

References
1) G. B. Barton, J. L. Hepworth, E. D. McClanahan, R. L. Moore, H. H. Van Tuyl, “Chemical
processing wastes; Recovering fission products,” Ind. Eng. Chem., 50[2], 212-216 (1958).
2) K. Watari, M. Izawa, “Separation of radiocesium by copper ferrocyanide-anion exchange
resin,” J. Nucl. Sci. Technol., 2, 321-322 (1965).
3) K. Watari, K. Imai, M. Izawa, “Radiochemical application of iron ferrocyanide-anion
exchange resin,” J. Nucl. Sci. Technol., 5, 309-312 (1968).
4) K. Tanihara, “Preparation of insoluble hexacyanoferrate(II)-macroporous ion exchange
resin composites and comparison of their performance as a regenerable ion exchanger for
cesium,”Nippon Kagaku Kaishi, 9, 835-841 (1996), [in Japanese].
5) K. Tanihara, “Selective separation of cesium from strongly acidic nitrate media by
repeated use of cupric ferrocyanide-silica gel composite ion exchanger of redoxtype,”
Reports of the Kyushu National Industrial Research Institute, No. 61, 23-28 (1998).
6) H. Mimura, M. Kimura, K. Akiba, Y. Onodera, “Selective removal of cesium from highly
concentrated

sodiumnitrateneutralsolutionsbypotassium

nickelhexacyanoferrate(II)-loaded silica gels,” Solvent Extr. Ion Exch., 17, 403-417 (1999).
7) H. Mimura, M. Kimura, K. Akiba, Y. Onodera, “Separation of cesium and strontium bypotassium hexacyanoferrate(II)-loaded zeolite A,” J. Nucl. Sci. Technol., 36, 307-310(1999).
8) K. Saito, T. Sugo, Delicious Recipe for Graft Polymerization, Maruzen, Tokyo (2008), [inJapanese].
9) S. Asai, K. Miyoshi, K. Saito, “Modification of a porous sheet (MAPS) for thehigh-performancesolid-phaseextractionof traceandultratrace

radiation-induced graft polymerization,” Anal. Sci., 26, 649-658 (2010).
6

elementsby10) K. Ikeda, D. Umeno, K. Saito, F. Koide, E. Miyata, T. Sugo, “Removal of boron using
nylon-based chelating fibers,” Ind. Eng. Chem. Res., 50, 5727-5732 (2011).

7

Figure captions

Fig. 1

Two preparation schemes of cobalt-ferrocyanide (Co-FC)-impregnated fiber

Fig. 2

XRD patterns of 6-nylon, VBTAC-Co-FC, and SSS-Co-FC fibers(a) 6-nylon, (b) VBTAC-Co-FC fiber, (c) SSS-Co-FC fiber; the peaks identified by ▽correspond to K2CoFe(CN)6

Fig. 3Distributions of Fe and Co across ferrocyanide-ion-bound VBTAC fiber and
VBTAC-Co-FC fiber(a) Fe across ferrocyanide-ion-bound VBTAC fiber, (b) Fe across VBTAC-Co-FC
fiber, (c) Co across VBTAC-Co-FC fiber8

Fig.1

Two preparation schemes of cobalt-ferrocyanide (Co-FC)-impregnated fiber

R. Ishihara:
Removal of Cesium Using Cobalt-Ferrocyanide-Impregnated Polymer-Chain-Grafted Fibers

9Fig.2

XRD patterns of 6-nylon, VBTAC-Co-FC, and SSS-Co-FC fibers(a) 6-nylon, (b) VBTAC-Co-FC fiber, (c) SSS-Co-FC fiber; the peaks identified by ▽correspond to K2CoFe(CN)6

R. Ishihara:
Removal of Cesium Using Cobalt-Ferrocyanide-Impregnated Polymer-Chain-Grafted Fibers

10Fig.3Distributions of Fe and Co across ferrocyanide-ion-bound VBTAC fiber and
VBTAC-Co-FC fiber(a) Fe across ferrocyanide-ion-bound VBTAC fiber, (b) Fe across VBTAC-Co-FC
fiber, (c) Co across VBTAC-Co-FC fiber

R. Ishihara:
Removal of Cesium Using Cobalt-Ferrocyanide-Impregnated Polymer-Chain-Grafted Fibers

1112