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from 12.5 to 13.5, have high ionic strengths, and are dominated by Na and K in the early stage and
by Ca in the later stage. The high pH will change the pore water chemistry which might affect the
mineralogy of the interacting phases.
All the above mentioned processes may induce mineral alterations (dissolution, transformation or
precipitation) in the Boom Clay. The change in mineralogy and geochemical properties may affect
the suitable properties of the Boom Clay as an effective barrier against radionuclide migration. The
objective of the SMARAGD project is to provide high quality data for performance assessment calculations.
Based on these calculations a judgement can be passed on the extent and the importance
of mineralogical alterations on the overall performance of the Boom Clay as a geological barrier
from long-term perspective.
2. Materials and methods
All the samples for the study of the oxidation were taken from the underground research facility
HADES in Mol, Belgium. The clay around the gallery was sampled by means of stainless steel cutting
edges. The cutting edge in the Test Drift was taken between rings 41 and 42 to the East (TD
R41-42E), the cutting edge in the Connecting Gallery was taken between rings 68 and 69 to the
East (CG R68-69E). For the detailed analyses of the effects of oxidation on the clay close to the
gallery lining, both clay cores (TD R41-42E and CG R68-69E) were cut into thin slices. For each
clay core, the first 10 cm of clay was cut into slices of 2 mm. The slicing of the clay core was performed
in an anaerobic glovebox with a controlled CO2 atmosphere. The mineralogy of the solids
was investigated by means of XRD, FTIR and SEM techniques.
In order to study the effects of an alkaline plume on the Boom Clay mineralogy, the bulk rock
Boom Clay powders were interacted with Young Cement Water (YCW) and Evolved Cement Water
(ECW) simulating the early and evolved alkaline fluids released from water-saturated concrete.
The YCW is highly alkaline (pH = 13.5) solution dominated by K (5500 ppm) and Na (1490 ppm),
while ECW is less alkaline (pH = 12.5) with Na and Ca as dominating cations (440 and 409 ppm
respectively). The PE bottles were charged with 10 g of powdered Boom Clay and 121 ml of the
reagent solution. The bottles were put inside the oven and left at a temperature of 60°C. After specific
time intervals (90, 180, 360 and 510 days), the samples were withdrawn, and the solids were
separated from solutions by centrifugation and filtration. The solid leftovers were subject to XRD,
FTIR and SEM investigation. In addition, cation exchange capacity and surface area measurements
were performed on the selected Boom Clay samples at the end of the alkaline plume batch experiment.
3. Results
The mineralogical study of the oxidized samples from HADES URL showed that gypsum
(CaSO4.2H2O) was formed in the clay close to the gallery lining, both in the samples from Test
Drift and the Connecting Gallery based on XRD investigation (Fig. 1). Its presence is limited to the
first ~4.6 cm from the concrete/clay interface in the Test Drift and to the first ~4.2 cm from the
concrete/clay interface in the Connecting Gallery. Further away from the concrete lining, the XRD
patterns approach those of the undisturbed rock. In the Connecting Gallery, jarosite
(KFe3(SO4)2(OH)6) was identified in the clay close to the gallery lining by means of XRD technique.
In contrast, jarosite was absent in the samples from the Test Drift (Fig. 1). Calcite was not
detected in the clay close to the gallery lining in the samples from the Connecting Gallery, while it
was present in the Test Drift. The solid residuums of the Boom Clay samples were analyzed by
XRD after 90, 180, 360 and 510 days of the interaction with YCW and ECW (Fig. 2). The everpresent
change is the progressive decrease of the pyrite intensity in every studied sample. The py-
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