2021 年 55 巻 4 号 p. 110-121
Radiocesium was emitted into the environment due to the Fukushima Dai-ichi nuclear power plant accident, and it is strongly adsorbed by surface soil. The large-scale decontamination was succeeded. But a serious problem remains, i.e., long-term storage of a massive amount of the waste soil provided by the decontamination. It is known that micaceous clay minerals are the primary adsorbents of radiocesium in soil. Scientific knowledge of the states and mechanisms of cesium adsorption to micaceous clay minerals is required to develop volume reduction techniques and safe long-term storage. However, it is not easy to reveal them only by the experimental study because the adsorption is intrinsically a microscopic phenomenon that is difficult to be approached even by recent advanced experimental techniques. Numerical simulation is one of the best techniques to investigate microscopic phenomena. We developed the models of the five adsorption sites in the micaceous clay minerals: basal surfaces, edges, hydrated interlayers, frayed edges, and interlayers. The outline of the simulations of these adsorption sites is briefly reviewed. Particularly, the mechanism of the origin of the strong adsorption of cesium to frayed edge sites is discussed based on the results of our numerical simulations. A future direction of numerical simulations of clay minerals is shown.