Bentonite Mineralogy Part 1: Methods of Investigation - Posiva

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001 peak is sensitive to the relative humidity in the laboratory during the X-ray runs
because the humidity affects the number of water layers in the interlayer position.
During the runs the relative humidity was monitored and it ranged from 55 to 60%.
6.1.2 Fractionation, saturation and preparation of oriented aggregates
Fractionation was done by suspending gently ground samples in deionized water and
letting them settle for 16-20 hours in 100 - 150 ml decanter glasses. No dispersing
agents were used to avoid the exchange of interlayer cations of smectite minerals. The
aim was to separate fraction< 1 J..Lm. Only couple of samples (Kutch 8939, Kutch 8940,
Friedland, Skalna, Dnesice) could be fractionated like that. Three samples, all Ca,Mgmontmorillonites
(Milos high-grade, Rokle, Strance) settled quickly and had to be
washed free of electrolytes before fractionation. Most Na-montmorillonites formed gellike
suspension. A small part of the gel from the top layer was mixed with deionized
water and centrifuged (1 0 min, 2000 r/min). The uppermost part of clay was used for
the preparation of oriented aggregates that were done by spreading the gel on a glass
slide and letting it dry at room temperature. The gel from the decanter glasses was dried
for further use (FTIR and TEM). The exact grain size is unknown. Part of the fraction<
1 J..Lm, when possible to separate it, was used for oriented aggregates that were prepared
using the filter transfer method (see 3.1.1). The rest of the fraction was centrifuged and
dried for further use (FTIR and TEM).
Two samples (Rokle & Strance) were saturated with Mg by mixing the bulk samples
with 2M MgCh and letting the mixture stay for 24 hours. After that they were washed
with deionized water by repeated centrifugations until the fine fraction remained in
suspension. The suspensions were fractionated and oriented aggregates were prepared
as described above.
The X-ray diffractograms of the air-dried oriented aggregates were recorded from 2 to
30°28. The counting time was 1 s per 0,02°28.
6.1.3 Solvation with ethylene glycol (EG) or glycerol (G)
After recording the diffractograms of air-dried aggregates they were placed in ethylene
glycol atmosphere at 60°C for 16-20 hours. The X-ray diffractograms were recorded
again from 2 to 30°20. Two oriented aggregates of Mg-saturated fine fractions were
solvated also with glycerol by mixing three drops of glycerol to the suspension in the
last phase of filtration. The oriented aggregate on the membrane filter was laid face
down on a glass slide and the filter removed carefully. The diffractograms were
recorded when the aggregates still were wet.
6.1.4 Calculation of 1/S content
The content of illitic layers in possible mixed-layer illite/smectite was estimated using
the method suggested by Moore & Reynolds (1997); see 3.1.5).