Effects of the injection grout Silica sol on bentonite

Abstract

Silica sol, i.e., colloidal SiO 2 , may be used as a low-pH injection grout for very fine fractures in the construction of deep geological repositories for radioactive waste in Sweden and in Finland. If the bentonite barrier encounters SiO 2 -colloid particles under conditions favorable for aggregation, there is concern that it will modify the bentonite barrier at the bentonite/bedrock interface. In this study qualitative experiments were performed with mixed dispersions of SiO 2 -colloids and bentonite or homo-ionic Na/Ca-montmorillonite. Samples were prepared at different colloid concentrations and treated under various conditions such as low and high ionic strength (0.3 M NaCl), as well as dehydration and redispersing. Free swelling and settling experiments were performed in order to qualitatively compare the conditions in which SiO 2 -colloids affect the bulk/macro properties of bentonite. In order to study specific SiO 2 -colloid/montmorillonite interactions and preferred type of initial aggregation, dilute dispersions of homo-ionic montmorillonite dispersions mixed with varying concentrations of SiO 2 -colloids were prepared and selected samples were characterized by PCS, SEM/EDS, AFM and PXRD. The results from this study show that bentonite and montmorillonite particles can be modified by SiO 2 -colloids when mixed in comparable amounts, due to dehydration or high ionic strength. Some indications for increased colloidal stability for the SiO 2 -colloid modified clay particles were also found. From the AFM investigation it was found that initial attachment of the SiO 2 -colloids in Na + dominated samples seemed to occur on the edges of the montmorillonite layers. In Ca 2+ dominated samples not subjected to excess NaCl, SiO 2 -colloid sorption onto the faces of the montmorillonite layers was also found. In all, contact between the bentonite barrier and ungelled Silica sol should preferably be avoided.

Effects of Temperature on the Deposition Rate of Supersaturated Silicic Acid on Ca-type Bentonite

“…5. Therefore, probably, chemically active sites on the surface of Ca-type bentonite mainly contribute to the deposition of silicic acid [22]. Conversely, significant amounts of colloidal silicic acid were formed when the amount of Ca-type bentonite was low, and the initial concentration of silicic acid was high, as shown in Figs.…”

Selection of Colloidal Silica Grouts with Respect to Gelling and Erosion Behaviour

“…Three different colloidal silica sols were chosen for this research as they have previously been studied in the work of the Chalmers University of Technology [8], the Äspö Hard Rock Laboratory in Sweden [9], and by Posiva Oy in Finland [10]. These grouts are Cembinder, Eka EXP36, and Meyco MP320 (Brand names: Bindzil 40/220, Bindzil 309/220 and Bindzil 40/170 from Akzonobel ® , Bohus, Sweden).…”

Innovative Technology of Horizontal Protective Shield Arrangement Using Injection

“…The glue properties of bentonite can be used for shield arrangement because they can prevent the spread of radioactive substances [29]. Moreover, bentonite may be used as a binder in injectable solutions because of its low dispersion [30,31].…”