Manuel Pozo Rodríguez

Alteration of compacted bentonite by diffusion of highly alkaline solutions

Compliance of concrete – bentonite barriers is a key issue in the performance assessment of long-term underground storage of radioactive waste. The reaction of synthetic alkaline solutions (K–Na–OH and Ca–(OH) 2 ) interacting by diffusion with a Mg-saturated compacted FEBEX-bentonite column of 2.1 cm thickness was investigated through closed-system experiments at 60 °C over 6 and 12 months. The first few millimeteres near the surface were grated to resolve mineralogical changes at sub-mm resolution determined by XRD, SEM, BET and the analysis of exchangeable cations. Alkaline cations diffused beyond the mineralogical alteration zone (2–2.5 mm), and were exchanged by Mg 2+ in the interlayer region of montmorillonite, but no K-silicates were formed. The presence of minor zeolites in the alteration assemblage was only detected by XRD on samples treated with ethylene-glycol. A cemented rim mixed with poorly ordered clay materials, mainly brucite, a chlorite-like phase and Mg-smectite was found at the interface. Montmorillonite was partially dissolved and a part of it remained shielded by the newly-formed cementation crusts. Cation diffusion through the interlayer of montmorillonite is inferred to be the dominant transport pathway in compacted bentonite equilibrated with external high pH solutions. The high pH front diffused at a much slower rate due to buffering of mineral reactions.

From democratic school to civic and political participation / De la escuela democrática a la participación política y ciudadana

Abstract The aim of this article is to study the possible influence that exercising a representative role at school may have on secondary school students’ willingness to participate politically in society. In order to do this, an analysis was carried out of the answers given by 300 students between 13 and 18 years old, from a school with marked democratic practices, when asked about their experience of democracy at school and their intention to participate politically. The results show that students’ willingness to participate in society by means of conventional actions, such as voting, does not depend directly on whether they have exercised a representative role at school. However, non-conventional actions, such as attending demonstrations or supporting boycotts, does have a meaningful relation with the exercise of representative roles in the school. As a conclusion, we highlight that participating in the representation of the school influences the democratic formation of students and their willingness to participate politically in society, although this influence is more closely related to non-conventional actions, such as strikes, boycotts and demonstrations.