Generation and stability of bentonite colloids at the bentonite/granite interface of a deep geological radioactive waste repository.
The possible mechanisms of colloid generation at the near field/far field interface of a radioactive repository have been investigated by means of novel column experiments simulating the granite/bentonite boundary, both in dynamic and in quasi-static water flow conditions. It has been shown that solid particles and colloids can be detached from the bulk and mobilised by the water flow. The higher the flow rate, the higher the concentration of particles found in the water, according to an erosion process. However, the gel formation and the intrinsic tactoid structure of the clay play an important role in the submicron particle generation even in the compacted clay and in a confined system. In fact, once a bentonite gel is formed, in the regions where the clay is contacted with water, clay colloids can be formed even in quasi-static flow conditions. The potential relevance of these colloids in radionuclide transport has been studied by evaluating their stability in different chemical environments. The coagulation kinetics of natural bentonite colloids was experimentally studied as a function of the ionic strength and pH, by means of time-resolved light scattering techniques. It has been shown that these colloids are very stable in low saline (approximately 1 x 10(-3) M) and alkaline (pH > or = 8) waters.
Missana
Tiziana
T
Departamento de Impacto Ambiental de la Energia, CIEMAT, Avenida Complutense, 22-28040 Madrid, Spain. tiziana.missana@ciemat.es
Alonso
Ursula
U
Turrero
Maria Jesús
MJ
D000538:Aluminum Silicates; D001546:Bentonite / Q000737:chemistry*; D000077215:Clay; D003102:Colloids / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D011850:Radioactive Waste; D012037:Refuse Disposal / Q000379:methods*; D012822:Silicon Dioxide / Q000737:chemistry*; D012990:Soil Pollutants, Radioactive; D014875:Water Pollutants, Radioactive
D000538:Aluminum Silicates; D003102:Colloids; D011850:Radioactive Waste; D012990:Soil Pollutants, Radioactive; D014875:Water Pollutants, Radioactive; C007886:granite; D001546:Bentonite; D012822:Silicon Dioxide; D000077215:Clay