Effects of Salinity and High pH in Crushed Rock and Bentonite:Experimental Work and Modelling in 2001 and 2002

The research work presented here includes the progress obtained in Finland in the two first years of the three-year ECOCLAY II project. The final results obtained in the project are reported in the fall 2003. Two types of experiments are carried out; flow-through experiments, which simulate one suggested backfill concept for the tunnel consisting of compacted bentonite and crushed rock, and batch experiments including sorption studies. Sorption is studied with two radionuclides, 45Ca and 22Na. Both types of experiments are conducted in anaerobic CO2-free atmosphere. In both experiments the solid materials used are the same; MX-80 bentonite (loose and compacted) and crushed crystalline rock powder from Olkiluoto disposal site in Finland. The solid materials are attacked by simple simulated groundwater compositions; synthetic solutions covering fresh alkaline (pH=12.5), saline alkaline (pH=12.5), and saline hyper alkaline (pH=13.5) conditions in order to simulate the effects of cement in the repository, but also fresh (pH=8.8) and saline (pH=8.3) conditions for comparison purposes. Some chemical changes occurring during and after the experiments are recorded in the sample solutions and bentonite pore water. Both bentonite and crushed rock powder are characterised prior to and after the experiments in order to facilitate the modelling of the alterations occurred in the solid phases after the attack of the different simulated solutions. The results of the batch experiments are used in the mechanistic sorption modelling of the fresh water/clay system. The results are also used in the quantification of the effect of increasing salinity on the extent of sorption, as well as, in the qualitative interpretation of the sorption mechanisms involved in the conditions studied. The flow-through tests aim at assessing the propagation of an alkaline plume in bentonite. All the information obtained from the mineral alteration studies (XRD, SEM/EDS, micro-probing) and solution chemistries facilitates the modelling (PHREEQC) of the alkaline attack on bentonite and crystalline rock contributing in quantification of the processes involved. Sensitivities of the thermodynamic databases for moderate water salinity variations are also considered in the view of data produced in the experiments

Identifying ‘climate keystone species’ as a tool for conserving ecological communities under climate change

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