Environmental Engineering Reference
In-Depth Information
3
oRiGin anD sTRUcTURe oF The
halloYsiTes
The halloysites are mainly formed as the result
of weathering of ultramafic rocks, volcanic glass
and pumices. The samples analysed in this study
came from the alteration of piroclastes of basic
characteristic.
They are clay minerals belonging to the group
of kaolinites. its principal characteristic is that
the plates are separated by a monolayer of water
molecules. This structure is called halloysite
(10Å). as the forces that tie the water molecules
with the rest of the structure are weak, the clay
can be easily dewatered (by air drying, at vacuum
or by a light heating) and be irreversibly trans-
formed in halloysite (7Å). Due to that reason,
halloysite (7Å) is easily found near the surface
while halloysite (10Å) is detected at great depths.
Besides, the manipulation of the samples usually
induces that transformation (Joussein et al. 2005).
Figure 5 shows the halloysite clay material in its
natural state and after being dried in oven. The first
sample shows a cluster aspect while the second one
has a surface covered with little dewatering cracks.
This difference shows the great influence of water
content in the material.
halloysite particles can show a great number
of different morphologies. The most usual one
is a structure in elongated tubes with an average
Figure 6. Photographs taken with a microscope of
halloysite material: above, in tubular structure and
below with the structure resulting from a dehydratation
process.
diameter of 0.07 µm. The dehydratation has an
influence on the clay morphology: in the spheri-
cal structures it provokes diameter reduction of
particles, while it increases the diameter of tubular
shapes. Figure 6 shows two images, made in the
microscope, of an halloysite typical tubular struc-
ture and of a structure resulting from a dehydrata-
tion process.
4
iDenTiFicaTion TesTs
4.1
Grain size distribution tests
The 35 grain distribution tests by sieve that were
made showed a percentage of fine particles (par-
ticles smaller than 0.08 mm), between 65 and
95%, with a representative average value of 85%.
Particles greater than 2 mm were not detected.
Figure 7 shows the grain size distribution curves
obtained.
in all the samples, grain distribution tests by
sedimentation were also performed following the
spanish standard Une 103102-1995. With the
aim of being able to sieve the sample, the material
Figure 5. Photographs of the samples: above, in its natural
state and below, after being dried in oven.
