Journal of Environmental Radioactivity 140 (2015) 78e83

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Variation in available cesium concentration with parameters during temperature induced extraction of cesium from soil Durga Parajuli a, *, Akira Takahashi a, Hisashi Tanaka a, Mutsuto Sato b, Shigeharu Fukuda c, Ryuichi Kamimura c, Tohru Kawamoto a, * a b c

Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, 305-8565, Japan Fukushima Agricultural Technology Center, 116 Shimonakamichi, Takakura, Hiwada-machi, Koriyama, 963-0531, Japan Tokyo Power Technology Ltd., 5-5-13, Toyosu, Koto-ku, Tokyo, 135-0061, Japan

a r t i c l e i n f o

a b s t r a c t

Article history: Received 2 September 2014 Received in revised form 23 October 2014 Accepted 6 November 2014 Available online

Cesium extraction behavior of brown forest type soil collected from paddy fields in Fukushima nuclear accident affected areas was studied. In nitric acid or sulfuric acid solutions at elevated temperature, the concentration of Cs in soil available for extraction, m0, has been estimated on the basis of modified canonical equation and the equations derived from assumed equilibria. With the variation in temperature, mixing time, and soil to solvent ratio, the observed m0 values in 0.5 M acid solution ranged between 1.5 and 2.9 mg cesium per kilogram of soil. By increasing the acid concentration to 3 M, the value of m0 could be sharply increased to 5.1 mg/kg even at 95  C. This variation in the extractable concentration of cesium with the parameters signifies the existence of different binding sites in the soil matrix. The results observed for uncontaminated sample could be reproduced with the radioactive cesium contaminated sample belonging to the same soil group. © 2014 Elsevier Ltd. All rights reserved.

Keywords: Cs in soil Extraction Decontamination Canonical equation

1. Introduction Environmental mobility of the radioisotopes of cesium has been widely studied following its anthropogenic entry by nuclear testing and nuclear power plant accidents (Steinhauser et al., 2014; Lindblom, 1969; Anspaugh et al., 1988). Frayed edge sites in illite type clay minerals are known to bind the cesium (Cs) ion almost irreversibly (Francis and Brinkley, 1976). The decontamination task gets complex in the course of time owing to the transport of the Cs ion from more exchangeable sites to the almost irreversible sites (Comans, 1999; Cremers et al., 1988). Recent Fukushima Daiichi Nuclear Power Plant accident released approximately 1.8  1016 Bq Cs-134 and 1.5  1016 Bq Cs-137 contaminating thousands of square kilometers of land (IAEA, 2012; Stone, 2011; Chino et al., 2011). Since Cs radioisotopes are strong gamma emitters with the halflives of 2.06 y (Cs-134) or 30.1 y (Cs-137), amongst many other radioisotopes released from the nuclear accidents, its presence in the environment imposes long lasting impacts (IAEA, 2006;

* Corresponding authors. Tel.: þ81 29 861 5141. E-mail addresses: [email protected] (D. Parajuli), tohru.kawamoto@aist. go.jp (T. Kawamoto). http://dx.doi.org/10.1016/j.jenvrad.2014.11.005 0265-931X/© 2014 Elsevier Ltd. All rights reserved.

Toxicological Profile, 2004). Therefore, as an immediate relief, topsoil removal is considered. The task of scrubbing the surface soil is certainly difficult and more difficult is long term monitoring of the removed contaminated soil. According to a report, topsoil removal tested around Fukushima reduced as high as 80% Cs activity, while this process generated 3-4t waste soil per acre land (MAFF, 2011). As a consequence, thousands of tons of removed soil are accumulated around the Tohoku and Kanto area of Japan. Separating the clay portion out of soil greatly reduces the volume, only if the Cs radioisotopes are totally adhered to the clay minerals. However, given the variation in distribution of Cs in various soil groups depending upon the geochemical circumstances, Cs extraction from soil overall is considered preferable for achieving effective decontamination (Koarashi et al., 2012). Following the radioactive fallout and Chernobyl disaster, there have been detail studies on Cs extraction from soil. However, the peculiar interaction of Cs with various soils has attracted more interest, though studies on Cs removal like chemical extraction, use of microorganisms, and phytoremediation were also performed with limited success (Hendricks et al., 1940; Wendling et al., 2004, 2005; Dushenkov et al., 1999). Also, methods demonstrating high Cs extraction for the soil collected in one region are found to be not necessarily effective for the similar kind of soil sampled from

D. Parajuli et al. / Journal of Environmental Radioactivity 140 (2015) 78e83

different region (Vandebroek et al., 2012). So, this study is aimed for the understanding of Cs extraction equilibria for brown forest type soil, which is widely distributed in the Fukushima region.

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150  C and 200  C. The effect of mixing time, acid concentration, and soil to solvent ratio were studied at 95  C. All the extraction experiments were performed at least three times and the average values are used for the discussion.

2. Materials and method 3. Results and discussion

2.1. Soil characteristics Sample BFS-Ii, a paddy field soil free of radioactive Cs, belonging to Brown Forest Soil (BFS) type and umbisol or cambisol reference group was collected from the Iitate (Ii) village in Fukushima prefecture. For the preliminary Cs extraction studies, the sample was dried at 105  C for 24 h and sieved to

Variation in available cesium concentration with parameters during temperature induced extraction of cesium from soil.

Cesium extraction behavior of brown forest type soil collected from paddy fields in Fukushima nuclear accident affected areas was studied. In nitric a...
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