Photon Factory Activity Report 2018 #36 (2019)

BL-27B/2016G637,2018G567

EXAFS analysis of temperature dependence of cesium adsorption in the sediment atLake Onuma on Mt. Akagi
Naoto Kumagai1 , Takamasa Nagahashi1, Haruaki Matsuura1*,
Takafumi Uchiyama1, Kyuma Suzuki2, Shun Watanabe2, Hajime Arai2,
Kin-ichi Tsunoda3 and Yukiko Okada1
1

Cooperative Major in Nuclear Energy, Tokyo City University,
1-28-1 Tamazutsumi, Setagaya-ku, Tokyo, 158-8557, Japan2
Gunma Prefectural Fisheries Experimental Station,
13, Shikishima-cho, Maebashi, Gunma, 371-0036, Japan
3Gumma University, 1-5-1, Tenjin-cho, Kiryu, Gunma, 376-8515, Japan

2 Experiment
The sediment was dried at room temperature, 50 °C,70 °C, 100 °C, 150 °C. for 24 hours. Five samples(room temperature, 50 °C, 70 °C, 100 °C, 150 °C) wereadded to 1 M CsCl solution, stirred for 1 hour, allowed tosettle for 24 hours to adsorb cesium, filtered from liquidand each temperature (room temperature, 50 °C, 70 °C,100 °C, 150 °C). EXAFS measurement was carried out at
High Energy Accelerator Research Organization Photon
Factory BL-27B, in transmission mode, using CsLIIIabsorption edge.
3 Results and Discussion
Cesium dissolved in water is bonded via oxygen of 8
water molecules. In addition, cesium ion specificallyadsorbed by clay minerals such as layered silicates forms

much stabilized as an inner-sphere complex than hydrated
state in solution [2].
Figure 1 shows that structural functions of Cs adsorbed
on five samples (room temperature, 50 °C, 70 °C, 100 °C,
150 °C). The peak of the first neighbor is a bond withoxygen of hydrated water, i.e.,2.3 Å. The peak of thesecond neighbor is considered to be oxygen of the clay
minerals, i.e., 3.5Å. This peak shows that thecoordination number increased as the drying temperature
increased. It was suggested that there is a correlation
between drying temperature of sediment and Cs
adsorption.
RT
50℃
70℃
100℃
150℃

FT|(k)·k3| [arb.unit]

1 Introduction
In the Lake Onuma on Mt. Akagi, exceeding
radioactivity of cesium over the standard value had been
still detected from the lake water and aquatic lives due tothe Fukushima Daiichi Nuclear Power Plant accident.
Currently radioactivity of water decreased under thestandard value, but a decreasing trend of the radioactivityof cesium of the lake was being slowly after 2015 [1].
Since the continuous survey of the lake shows that
dissolved Cs is dominant of radioactivity at a bottom oflake, we conjecture that radioactive cesium might beeluted from bottom of lake sediment. The adsorption
experiment of radioactive cesium with sediments wasconducted and it was found that about 70% of it wasadsorbed. However, drying the sediment at 100 °C prior
to the adsorption experiment suggested that the particle
size may change due to drying, possibly underestimating
cesium adsorption. Therefore, temperature dependence ofadsorption was investigated by conducting stable cesium
adsorption experiments using sediments dried at room
temperature, 50 °C, 70 °C, 100 °C, and 150 °C. In orderto evaluate the adsorption of cesium-adsorbed sediment,
we have investigated the local structure of cesium insediment by EXAFS.

01234R [Å]Fig. 1: Structural functions of Cs-adsorbed sedimentswith different drying temperatures.

Acknowledgement
This work was financially supported by the JSPS
KAKENHI Grant Number JP26292100, JP18K04995.
References[1] K. Suzuki et al, The Japanese Society of Fisheries
Science, 82, 774-776（2016)[2] Y. Takahashi et al. Surface science. Vol.34, No.3,pp.122 (2013)* hmatuura@tcu.ac.jp