Bentonite Mineralogy Part 1: Methods of Investigation - Posiva

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4) Another recommended method is preparation on porous plate. However, this method
is not used in Finland.
3.1.2 Solvation and heating
The aggregates are dried at room temperature and the XRD patterns recorded. The
identification of expandable clay minerals includes solvation with ethylene glycol or
glycerol that are able to enter the interlayer positions. The recommended method is to
keep the clay aggregate for long enough time in ethylene glycol (EG) vapour at elevated
temperature (24 hat 80°C, Driefet al., 2001; at least 48 hours at 60°C, Olsson, 1991; at
least 8 h at 60°C, Moore & Reynolds, 1997; 12 hours at 70°C, Claret et al., 2002).
Glycerol solvation has to be done by adding a drop of liquid on the wet clay aggregate
and letting it almost dry. This can disturb the orientation and the quality of pattern is
often poor, because the aggregate has to be run wet. Solvation with EG shifts the lowcharge
vermiculite and smectite 001-peak position from 12- 15 A to 16- 17 A.
Glycerol solvation shifts the 001-peak of Mg-saturated smectite to 17- 18 A whereas
the vermiculite 00 1-peak remains unchanged at 14 - 15 A. Heating both vermiculite and
smectite to 300°C and higher temperatures causes dehydration and shifts the 001-peak
to 10 A.
Examples of preparation and solvation methods used in bentonite research:
- Inoue et al. (1987): The < 1 J-lm fraction of untreated clay samples was isolated by
centrifugation. The suspensions were smeared on glass slide, dried at room
temperature, solvated with ethylene glycol (EG) vapor, and examined by XRD
- Drief et al. (2002): The< 2 J-lm fraction was isolated, smeared on glass slide, dried at
room temperature, solvated with ethylene glycol at 80°C for 24 h, heated at 550°C
for 1 h
- Churchman (2002): EG-solvation: The aggregates were placed in a vacuum
desiccator over ethylene glycol liquid and left there for at least 2 days. Saturation
with Mg on membrane filter: The sample on the filter was covered twice with 1 M
MgCh for at least 10 min, the excess electrolytes were removed by washing with
deionized water at least three times.
- Kirsimae et al. (1999): XRD slides were obtained by sedimentation on a porous
porcelain plate under pressure or by smearing on a glass slide (sub fractions of the <
2J.!m material: 2-0,6, 0,6-0,2, 0,2-0,06 and < 0,06 J-lm). Solvation with ethylene
glycol vapour: 60°C, 48 h. Heat treatment: 525°C, 2 h. Mg-exchange: 1 M MgCh
overnight.
3.1.3 060 reflections
The d-value of the 060 (06-33) reflection of clay minerals is used for distinction
between dioctahedral and trioctahedral types. This is because the cell b-dimension is
sensitive to the size of the cation and the site occupancy in the octahedral sheet. The
d(060) value of dioctahedral minerals like kaolinite and muscovite is around 1,49 A