Geoscience Reference
In-Depth Information
3.4.3 Chemical Dissolution
Put simply, dissolution here is the ensemble of phenomena that chemically
attack the particles of various sizes, whether through true solubilization
or by hydrolysis. For simulating this we shall assume the particles to
be spherical. This change in shape and even more the fact of assigning
a regular and arbitrary shape to the particles in the models should not
shock the reader. It can be demonstrated by simulation and also proved
mathematically that the hypotheses based on the shape of the particles
have practically no effect on the results obtained. Dissolution will consist
of solubilizing a film of thickness
dl
around each particle in time
dt
(Fig. 3.17). This leads to losses in solution, which can be determined.
In the computer procedure, as before, the particles are sorted by
size in a table. For example, the particles of diameter 200
ยต
m will be
in box no. 200. Dissolution being gradual, it consists of translocating
the particles from box to box without ever skipping a box. The process
comes to a halt when the thickness taken off is
dl
.
Model
Dissolution by removal of a
thickness around each
particle during time
dl
dt
Losses in solution
Toward box
no. 1 (clay)
Computer representation of the dissolution
Toward box no. 2000
(coarse sands)
Losses in solution
Fig. 3.17
Model of dissolution of the skeleton grains.
The result of chemical solution appears paradoxical. To show this, let
us start with a collection of particles containing sands, silts and clays
at the same time, the point representing which is located at the centre
of the textural triangle (Fig. 3.18, left half, point X). Intuitively, since
each particle reduces in diameter, we could expect evolution towards
clay particles. But in reality, the smallest particles have a greater surface
area/mass ratio. They are therefore more susceptible to dissolution and
disappear in greater proportion by weight. The result is a trajectory
towards the sand corner, of course at the cost of a very pronounced loss
