Within the EC-funded SMARAGD project boom clay was studied as undisturbed rock and after geochemical perturbations (the alkaline plume and the oxidation effects). The most important messages of the project results are summarised in the paragraphs below. Quartz, K-feldspar, Na-pagioclase, pyrite, and carbonates are the principal non-clay mineral constituents; kaolinite, mica, mixed-layered I-S, and chlorite were identified as clay minerals in boom clay by qualitative XRD. In the framework of the mineralogical characterisation of the undisturbed boom clay, a novel QXRD (quantitative X-ray diffraction) technique was applied in order to quantify the relative abundances of the mineral constituents in the boom clay. This technique was used by two independent research groups (SCK•CEN and KU Leuven) at the same time so as to verify the reproducibility of the technique. In general, a good consistency was observed comparing the two data-sets for clay and non-clay mineral phases; however, quantification of the amorphous matter still remains a challenge. The quantitative mineralogical composition of the boom clay may vary significantly from sample to sample. The total non-clay content was found to vary in the range 41-77 weight-%; the total clay content from 23-59 weight-% in the studied sedimentary profile. The quantitative mineralogical composition is granulometry-dependent. The variations in CEC values measured by the Cu-trien method seem to follow the variations in the grain size distributions; the lowest CEC value (13 meq/100 g) being determined in course silt and the highest CEC (27 meq/100 g) found in the silty clay sample. The alkaline perturbation triggered distinct changes in the chemical composition of the leachates and in the mineralogy and physico-chemical characteristics of the boom clay. The degree of the geochemical perturbation induced by the alkaline solutions is mostly governed by the initial concentration of the OH- groups in these solutions, i.e. dependent on the base strength. The results indicate that the higher the initial pH of the media, the stronger its interaction with boom clay. This suggests in turn that the buffering capacity of the boom clay is relatively weak at high pH. The degree of the Si leach from boom clay follows the order 0.1 mol/l NaOH > YCW > 0.1 mol/l KOH > ECW > 0.1 mol/l Ca(OH)2; the same trend is applicable to sulphates and TOC contents in the analysed leachates. Furthermore, sulphates and TOC contents are highly correlated in the 0,1 mol/l NaOH, ECW and 0,1 mol/l Ca(OH)2 solutions. This points to close relationship between organic matter and pyrite in the boom clay. No correlation being observed in the K-dominated solutions indicates a different process (possibly K-fixation in clays) affecting the decomposition of the organic matter in the boom clay under high pH conditions. The concentrations of Al decreased in the series YCW > 0.1 mol/l KOH > 0.1 mol/l NaOH > 0.1 mol/l Ca(OH)2 > ECW. The inventory of the Na, K and Ca was probably controlled by the ion exchange reactions in the beginning and by the dissolution/precipitation of Na-Ca plagioclase, K-feldspars, and carbonates in the later stages of the experiment. The most significant changes in the mineralogy of boom clay caused by the alkaline plume perturbations involve the alteration of Na-Ca plagioclases to K-feldspars, the precipitation of gypsum in Ca-rich solutions, the dissolution of quartz in 0.1 mol/l NaOH environment, and the dissolution of clay minerals (mainly mixed-layered illite-smectite) in every studied case except for ECW. Worth to mention is that no illitisation was observed. The dissolution of clays is accompanied by the redistribution of the layer charge, followed by a decrease in the CEC (due to clay dissolution) and the specific surface area (dissolution of clay layers from stacks) parameters. The oxidation effects were studied on the clay cores taken from the Connecting Gallery (5 years old) and the Test Drift (about 20 years old). Comparing the two data-sets, the general conclusions could be drawn with respect to the degree and the extent of the oxidation at different times. The mineralogical evidence for the oxidation is traceable within the first ~4.5 cm ahead from the gallery lining both in the Test Drift and the Connecting Gallery. Gypsum as the most common oxidation product of pyrite was found in the both data-sets, while jarosite was found exclusively in the Connecting Gallery. Although the conditions might have been different in the two studied places, no mineralogical evidence was found in favour of the possible relationship between time and the extent of the oxidation phenomena.
