Alteration and dissolution of Na-montmorillonite in simulated groundwaters
- PDF / 179,968 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 108 Downloads / 163 Views
Alteration and dissolution of Na-montmorillonite in simulated groundwaters E. Myllykylä1, M. Tanhua-Tyrkkö1 and A. Bouchet2 1 VTT Technical Research Centre of Finland, P.O.Box 1000, 02044 Espoo, FINLAND 2 Etudes Recherches Matériaux ERM, Centre Régional d'Innovation du Biopôle, 4 rue Carol Heitz, 86000 Poitiers, FRANCE
ABSTRACT This study aims at gaining a better understanding of the behaviour of montmorillonite in contact with different ground waters; alteration of montmorillonite and possible formation of secondary minerals. Batch experiments were conducted with purified Swy-2 montmorillonite in simulated fresh (I=0.05 M, pH 8) and saline (I=0.1 M, pH 11) waters at 25 and 60ºC in anaerobic (Ar(g)) conditions. The concentrations of Al, Fe; Mg and Si were analysed from ultra-filtered solution samples with HR-ICP-MS (High Resolution Inductively Coupled Plasma Mass Spectrometry). The amount of released Si depended strongly on the experimental conditions. The Si concentrations at 60oC in the saline and fresh waters showed a difference greater than an order of magnitude. The initial purified montmorillonite and the solid materials from experiments were analysed with XRD. The analysis indicated that the nature of smectite did not change, but the experimental conditions, more or less, modified the structure of montmorillonite, e.g., in fresh waters the XRD spectra showed peaks typical of mixed layer minerals, which can refer to the presence of either randomly ordered illite/smectite or randomly ordered collapsed smectite/ hydrated smectite layers. The dissolution of montmorillonite was studied also by modelling with TOUGHREACT. The experimental and modelled results were compared revealing a need to develop the model e.g. in respect of the evolution of pH. INTRODUCTION The behaviour of bentonite in varying groundwater conditions is an essential part in the safety assessment of a KBS-3 nuclear waste repository concept. The crucial properties of bentonite for geological disposal, like high swelling capacity and high cation exchange capacity, are greatly based on the properties of bentonite's main mineral component, montmorillonite. However, many of the process studies so far have concentrated on bentonite, which also contains accessory mineral, whose presence substantially complicates the interpretation of the analysed data. For modellers, it would be important to gain data, with error marginals and interpretation options as little as possible. However, generally the initial solution composition in process studies, e.g., leach- experiments, has been chemically too complex. In addition, the concentrations of Al and Fe have mostly been so low, that their concentrations could not be analysed reliably. This study consisted of batch experiments conducted with purified montmorillonite in two different simulant waters at temperatures of 25ºC and 60ºC under anaerobic conditions. The compositions of simulant waters used in experiments were based on the prevailing or presumable groundwater conditions in the Olkiluoto Island, which is
Data Loading...
