Mineralogy and kinetics of alteration of a mixed-layer kaolinite/smectite in nuclear waste disposal simulation experiment (Stripa site, Sweden)

Abstract

A cylindrical core of “4a clay” (French clay material tested for the use in nuclear waste disposal sites) was placed in granite and heated along its central axis at 175°C for four years. In the hottest regions of the core, a hardened black coating was formed at the contact with the heater. In this coating, the original mixed-layer kaolinite/smectite was replaced by pure smectitic material; the minor phases (kaolinite, quartz, calcite,…) disappeared while anhydrite and gypsum crystallized. In the less altered regions of the core, both the original minerals and the reaction products were found. A semi-quantitative approach provides evidence for reactions characterized by different kinetics rates.