Cs–sorption in weathered biotite from Fukushima granitic soil

Abstract

The sorption characteristics of cesium (Cs) ions into weathered biotite with biotite-vermiculite interstratification collected from weathered granodiorite in Fukushima Prefecture, Japan has been investigated. Both single crystals and crushed powder forms of the weathered biotite were experimentally reacted with 20-2000 ppm CsCl aqueous solutions, and analyzed by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) to examine the distribution of Cs inside the crystals. From the XRD pattern, the proportion of vermiculite unit layers in the weathered biotite was estimated at~12%, with a tendency for segregation, and the whole XRD pattern was explained by the coexistence of biotite and vermiculite packets as well as the interstratified regions. Powder XRD of Cs-sorbed specimens showed that the 14.9 Å peak of the vermiculite packets was weakened at a low Cs concentration in the solution. Single crystals of the weathered biotite with a polished edge-surface were immersed in the CsCl solutions and examined using SEM and high-angular annular dark field (HAADF) imaging in STEM. Cs was not only incorporated in the vicinity of the exposed surface but also penetrated deeply inside the crystals. These analyses and observations revealed the Cs-sorption process in weathered biotite. At first, Cs preferentially replaced specific vermiculite interlayers in the vermiculite packets. With a higher Cs concentration in the solution, the Cs-substituted vermiculite interlayers increased in the vermiculite packets, and vermiculite layers interstratified in biotite also incorporated Cs.

Radiocesium interaction with clay minerals: Theory and simulation advances Post–Fukushima

“…One of the most important observations regarding radiocesium adsorption in Fukushima soils is that weathered biotite is a primary adsorbent Mukai et al, 2014Mukai et al, , 2016aMukai et al, , 2016bKikuchi et al, 2015). For example, recent experiments showed that illite and weathered biotite are the primary radiocesium-bearing phases in silt-and sand-size fractions of Fukushima soil (Tanaka et al, 2018).…”

“…For example, recent experiments showed that illite and weathered biotite are the primary radiocesium-bearing phases in silt-and sand-size fractions of Fukushima soil (Tanaka et al, 2018). Note that biotite in this article is defined as a Fe-rich phlogopite and/or a Mg-rich annite with the chemical formula K(Mg,Fe) 3 AlSi 3 O 10 (F,OH) as identified by X-ray diffraction (XRD), energy dispersive X-ray spectrometry (EDS) and TEM (Kikuchi et al, 2015;Mukai et al, 2016a). Although some observations prior to the Fukushima accident had identified the potential importance of weathered biotite as a Cs adsorbent (Sawhney, 1966;McKinley et al, 2001McKinley et al, , 2004Zachara et al, 2002), this observation is particularly critical in the Fukushima case because weathered granite, which contains weathered biotite, is a dominant source rock in the Fukushima area (Kikuchi et al, 2015;Mukai et al, 2016b;Takahashi et al, 2017).…”

“…In particular, Cs readily incorporates in anhydrous vermiculite interlayers and tends to segregate itself by almost full monoionic replacement in some interlayer spaces (Kogure et al, 2012). Furthermore, exposure to artificially high Cs concentrations was shown to cause a collapse (dehydration) of the interlayers of weathered biotite collected from the Fukushima Prefecture (Kikuchi et al, 2015). Finally, small-angle X-ray scattering (SAXS) studies revealed differences between the mesoscopic structural changes of vermiculite and weathered biotite caused by Cs adsorption (Motokawa et al, 2014a); in particular, experimental results indicate that weathered biotite contains wedge--shape interlayer structures, i.e., FES structures similar to those of illite ( Fig.…”

Weathered Biotite: A Key Material of Radioactive Contamination in Fukushima

“…This paper reviews our recent research with respect to WB in Fukushima, including its structure and Cs-sorption/desorption properties, and discusses the role of WB in the radioactive contamination in Fukushima. Details of the experiments to obtain the results presented here are described in the original papers already published (Mukai et al 2014(Mukai et al , 2016aKikuchi et al 2015;Motai et al 2016).…”

A structural coarse-grained model for clays using simple iterative Boltzmann inversion

“…Because of its ability to selectively exchange radiocesium, illite and similar clays have been investigated for the possibility of remediating radioactive plumes of cesium. 10 Despite extensive experimental study of ion adsorption at the frayed clay edge and exchange of ions in the clay interlayer [7][8][11][12][13] , the exact mechanism of cesium uptake remains elusive. 14 It is especially unclear how cesium displaces potassium within the interlayer far from the edge in anhydrous interlayers for clays such as illite 11,[15][16][17] .…”