Molecular Mechanism of Heavily Adhesive Cs: Why Radioactive Cs is not Decontaminated from Soil

Abstract

Two years having passed since the nuclear crisis at Fukushima, radioactive 137 Cs with a half-life of ∼30 years has come to the forefront of our largest concern. To gain an insight into current unsuccessful 137 Cs decontamination from soil, heavily adhesive Cs adsorption, referred to as specific Cs adsorption here, is highlighted for layered clay minerals. Besides the interlayer Cs + cations, a population of Cs is able to adsorb on the surfaces of open nanospaces with their sizes of ∼0.3 and ∼0.9 nm, which are formed by one-and two-clay nanosheet insertion into interlayer spaces. They are adsorbed on the surfaces of the open nanospaces so strongly that they cannot be removed even by a hydrochloric acid solution of pH 1.0; these open nanospaces thus act as the specific Cs adsorption sites. The characteristic local molecular structures as a claynanosheet edge and a wedge-shaped frayed part available in the open nanospaces are responsible for the specific Cs adsorption. Radioactive 137 Cs that is not cleaned up after the decontamination work would originate from the specific Cs adsorption clarified in the present work.

Multi-Quanta Spin-Locking Nuclear Magnetic Resonance Relaxation Measurements: An Analysis of the Long-Time Dynamical Properties of Ions and Water Molecules Confined within Dense Clay Sediments

“…In that context, clay-water solid/liquid interfaces [3][4][5][6][7][8][9] were frequently investigated for two reasons. First, from a theoretical point of view, clay platelets are flat and atomically smooth with a well-characterized structure and atomic composition, leading to ideal models of solid/liquid interfacial systems.…”

“…First, from a theoretical point of view, clay platelets are flat and atomically smooth with a well-characterized structure and atomic composition, leading to ideal models of solid/liquid interfacial systems. Second, natural and synthetic clays are used in a large variety of industrial applications (drilling, heterogeneous catalysis [8], waste storing [9], food, paint and cosmetic industries), exploiting their various physico-chemical properties (gelling, thixotropy, surface acidity, high specific surface and ionic exchange capacity, water and polar solvent adsorption, swelling). Optimizing applications such as heterogeneous catalysis and waste storing requires quantifying the mobility of solvent molecules and neutralizing counterions inside the porous network of clay minerals.…”

Nuclear Magnetic Resonance Study of Cs Adsorption onto Clay Minerals

“…These silicates stabilize Cs on the surface and silicate sheets because of their negative charges. In particular, in the case of 2:1-type layer silicates, Cs is strongly adsorbed at frayed edge sites (FESs) [7][8][9][10]. In this context, it is necessary to understand the stabilization mechanism to analyze the structure of Cs in the clay surface, silicate sheet, and FESs.…”

Study of reversibility of self-assembly in saponite layered nanoparticles

“…It has been found that the above-mentioned two nanosheet insertion type local molecular structure, referred to as type B, appearing during self-assembly is associated with a number of global environmental issues [4][5][6]. For example, the characteristic local structures as a nanosheet edge and a wedge-shaped frayed part available in the voids of type B are responsible for site specific Cs adsorption [4,5].…”

“…For example, the characteristic local structures as a nanosheet edge and a wedge-shaped frayed part available in the voids of type B are responsible for site specific Cs adsorption [4,5]. Pore fluid in this local structure has been suggested to be related to earthquake slip weakening in plate-boundary faults [6].…”