Bentonite Mineralogy Part 1: Methods of Investigation - Posiva

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The Milos bentonites contain poorly crystalline smectite and the calculations gave too
high percentages of calcite and pyrite. Both could be corrected using chemical data
(Table 7 -16). The activated Milos bentonite contains an appreciable amount of quartz.
The quartz content cannot be calculated using chemical data because smectites are
silicate minerals. The percentages given for sample Milos A in table 7-15 are not much
more than a guess. Other methods need to be used for that sample. The same is true for
the Friedland sample. There are no factors determined for mixed-layer minerals.
All the Czech samples contain a considerable amount of iron oxides. Only a small part
of iron is bound to octahedral sheets of the smectite/mixed-layer mineral. The iron
oxide as well as the calcite contents could be corrected using chemical data (Table
7-16). According to Lego et al. (1995), ea 50% oftotal iron in the< 2 J.lm fraction of the
Rokle bentonite is as goethite. According to FTIR data, octahedral sheets of the Rokle
smectite contain more iron than the octahedral sheets of other Czech smectites (Fig.
7-13, Appendix 4). The smectite content of the Rokle bentonite suggested in table 7-15
is probably too high. The first calculations gave percentages around 60 but were based
on over-estimation of calcite and iron oxide content. The smectite/kaolinite ratio is not
easily determined. Both minerals are poorly ordered and have broad XRD peaks. It is
probable that the Rokle sample contains mainly smectite or a smectitic mixed-layer
mineral, as does the Strance sample. The Skalna and Dnesice samples contain mainly
kaolinite. According to FTIR data, the proportion ofkaolinite increases in order Rokle­
Strance- Skalna- Dnesice.