Geoscience Reference
In-Depth Information
be recovered and plan the original burying of the sachets accordingly.
Three specific kinds of test mineral have been employed.
Vermiculite, in which the exchange sites have first been saturated by
a single cation, say calcium, is placed in polyamide bags, made of an
non-degradable material manufactured to have a porosity of 20
µ
m.
The vermiculite may be mixed with pure quartz sand to promote free
drainage. The mouth of the bag is then heat-sealed. Once in position,
the vermiculite gives information on the processes in the soil. It can,
according to conditions,
Vermiculite (Ranger et al. 1992)
be destroyed, that is to say, dissolved slowly (pH<2.5),
be partially attacked (pH 2.5 - 5.0). It releases Si, Fe and Al.
As regards aluminium, two outcomes are possible: it is either
released and removed in the drainage water or it is slightly
displaced and is trapped in the interlayers of the clay mineral
during its degradation. This case corresponds to a progression
toward aluminous vermiculites,
exchange its calcium with other cations that are retained instead
and then determined (pH >5).
Crystals of calcite (pure calcium carbonate) are crushed and the lustrous
splinters obtained are used as test-mineral. The surface of the calcite,
the initial state of which is checked with the electron microscope,
reacts almost instantaneously to the characteristics of the water that
bathes it.
Calcite (Delmas et al. 1987)
When buried in tropical soils, kaolinite weathers rapidly, which points
to its tendency to disappear naturally from these soils (Cornu
et al.
1995).
Kaolinite
1.2.6 Lysimetry
Lysimeters are field equipment that enable recovery of the waters passing
through different soil horizons for analysis and study of what substances
are transported in solution or in suspension (Fig. 1.8).
