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cell dismantled after 6 months, room temperature Mössbauer spectra of the bentonite collected at
the interface shows a sextet (quadrupolar splitting: -0,27 mm/s; isomeric shift: 0,25 mm/s; hyperfine
field: 100-350 KOe) typical from goethite. In the FTIR spectra recorded for the iron oxide found at
the interface after 15 months, there is a doublet placed at 570 and 478 cm -1 . These bands are characteristic
from hematite. EDS analysis detected high contents of chlorine (up to 5% at. in some cases),
and traces of common elements present in bentonite either in goethite or in hematite.
Iron powder seems to undergo slight corrosion. In the cell dismantled after 6 months, Fe powder
kept metallic luster and no corrosion products could be identified on it. In the cell dismantled after
15 months, it was observed the existence of corroded and non-corroded areas in iron powder. EDS
analysis of corroded iron powder detected, in most cases, traces of chlorine (0.6% at.) and calcium
(0. 3% at.). Precipitation of chloride was not homogeneous and where it was found, a thin layer of
hematite ( -Fe2O3) (Fig. 5) and maghemite (�-Fe2O3), was grown (below 1 m in all cases). In this
stage, corrosion may continue, however to a lesser extend, as there is no water available at the interface.
mg Cl / Kg of dry bentonite
4000
3000
2000
1000
0
Hydration - 25ºC
6 months
15 months
Heater - 100ºC
Section III Section II Section I Interface
462
mg SO 2-
4 /Kg of dry bentonite
1500
1000
500
0
Hydration - 25ºC
15 months
6 months
Heater - 100ºC
Section III Section II Section I Interface
Figure 3. Movement of chlorides (left) and sulphates (right) along the bentonite block (aqueous extract
solid: liquid 1:8).
Figure 4. (Left) Backscattered SEM image of the Fe/bentonite interface in the six-month test;
(Right) SEM image of hematite found at the interface after 15 months of experiment.
4. Discussion
30 �m �m
Fe 31.4%
O 51.4%
Cl 5.2%
Si 6.8% %
at.
20 �m
Fe 33%
O 57.2%
Cl 3.24%
Ca 0.37% %
at.
The redistribution of water content along the bentonite column occurs soon after the beginning of
the experiment. Desiccation of bentonite causes the precipitation of chlorides and calcite and the
prevalence of anhydrous iron oxides over iron oxyhydroxides[2]. Chlorides and sulphates are hygroscopic
salts. They are known to significantly enhance the corrosion of mild steel at relative hu-