SMARAGD - The study of Mineral Alterations of clay barriers used for Radwaste storage and its Geological Disposal

SMARAGD was a 2-years postdoctoral fellowship (2006-2007) funded under EURATOM programme of EC in order to study mineral alterations of Boom Clay triggered by geochemical perturbations. Two types of geochemical perturbations were considered: oxidation due to excavation/ventilation of underground galleries and the alkaline plume effects due to application of concrete both in the gallery lining and as a part of the waste package design. The oxidation was studied on clay cores taken from the Connecting Gallery and the Test Drift of the HADES Underground Research Laboratory (Mol, Belgium). The effect of the alkaline plume was studied in the laboratory as a batch experiment. The extent of mineralogical alterations as a result of oxidation is limited to first ~5 cm ahead from the gallery lining both in the Test Drift and the Connecting Gallery. The mineral changes involve the formation of jarosite, gypsum and dissolution of calcite as a result of pyrite oxidation. The interaction between Boom Clay and high pH solutions triggered distinct changes in the mineralogy and physico-chemical characteristics of the Boom Clay. The dissolution of clays is accompanied by the redistribution of layer charge, followed by an overall decrease in the cation-exchange capacity and specific surface area.