Reaction of bentonites with pyrite concentrate after wetting and drying cycles at 80°C: relevance to radioactive waste (Radwaste) storage

Abstract

The mineral stability of two bentonites was studied in the presence of pyrite concentrate to simulate the possible reactions between the bentonite barrier used in a high-level nuclear waste (HLW) repository and host rock containing up to 5 wt.% of admixed pyrite. Smectite was the only bentonite mineral affected by pyrite treatment under the experimental conditions used. Bentonites reacted differently with pyrite due to the different nature of the smectites. The distinct crystal chemistry of the smectites controlled by the composition of the parent rocks influenced the smectite surface properties (cation exchange capacity and layer charge distribution) which resulted in a different response of the bentonites to pyrite treatment. A partial transformation of the original smectites into H-smectites represented the initial stage of smectite destabilization on acid attack. Rising non-equivalent isomorphous substitution in the octahedral sheets of the smectites enhanced smectite reactivity and thus the reaction between bentonite and pyrite, causing lower stability of the bentonite containing high-charge smectite.

Mineralogical and physico–chemical properties of bentonites from the Jastrabá Formation (Kremnické vrchy Mts., Western Carpathians)

“…Bulk bentonite from the Lieskovec deposit contained from 51 to 65 wt. % of dioctahedral Al-Fe rich smectite (montmorillonite) (Šucha & Kraus 1999;Andrejkovičová et al 2006;Osacký et al 2012).…”

“…The formation of bentonite deposits is mainly associated with alteration of volcanic glass-rich rocks (Kraus et al 1994;Moll 2001). The composition of the parent rocks (acidic rocks -rhyolites, intermediate rocks -andesites and basic rocks -basalts) may affect the crystal chemistry of smectites (Christidis & Dunham 1997;Osacký et al 2012). For instance, the Fe 3+ for Al 3+ substitution controls the crystal chemistry of smectites derived from intermediate rocks, whereas Mg 2+ for GEOLOGICA CARPATHICA, 2019, 70, 5, 433-445 Al 3+ substitution seems to be more important for smectites derived from acidic precursors (Christidis & Dunham 1997).…”