Abstract
The outline and important role of clay minerals for the geologic disporsal of radioactive waste are shortly described. Cation exchange properties between some kinds of H-clays and cations (Li, Na, K, Mg, Ca, Sr, Ba, Co) have been performed in batch experiments. Mg, Ca and Co ions are strongly adsorbed by clays. Kd values for clay minerals are in order of montmorillonite≥rectorite>sericite≥kaolonite>chlorite≅halloysite. Levels of adsorption factors of cations for montmorillonite and rectorite are about 10-100 times compared with those for crystalline rocks and thier minerals. Montmorillonite changed to mica, chlorite, and some non-sheet silicate minerals through interstratified minerals under hydrothermal conditions. Three kinds of interstratified minerals, rectorite (Na, Ca, Sr, Ba), tosudite (Li, Mg, Ni, Co) and mica/smectite (random; K, Rb, Cs), are formed under the existence of cations in montmorillonite. The conversion temperature of interstratified minerals from montmorillonite is different in each sample. The Al-rich sample is more reactive and changes to interstratified mineral phases at lower temperature than Al-poor one.
