TITLE:
Tracing Water Flow and Colloidal Particles Transfer in an Unsaturated Soil
AUTHORS:
Dieuseul Prédélus, Laurent Lassabatere, Artur Paiva Coutinho, Cédric Louis, Thomas Brichart, Erij Ben Slimène, Thierry Winiarski, Rafael Angulo-Jaramillo
KEYWORDS:
Colloidal Particle Transport, Microstructure, Modeling, Unsaturated Soil
JOURNAL NAME:
Journal of Water Resource and Protection,
Vol.6 No.7,
May
23,
2014
ABSTRACT: In recent
years, many studies have been carried out on colloidal particle transfer in the
unsaturated zone because they can be a risk to the environment either directly or
as a vector of pollutants. A study was conducted on the influence of porous media
structure in unsaturated conditions on colloidal particle transport. Three granular
materials were set up in columns to replicate a fluvio-glacial soil from the unsaturated
zone in the Lyon area (France). It is a sand, a bimodal mixture in equal proportion
by weight of sand and gravel, and a fraction of bimodal mixture. Nanoparticles of
silica (SiO2-Au-FluoNPs), having a hydrodynamic diameter between 50 and
60 nm, labeled by organic fluorescent molecules were used to simulate the transport
of colloidal particles. A nonreactive tracer, bromide ion (Br-) at a
concentration of C0,s = 10-2 M was used to determine the hydrodispersive properties of porous media. The tests
were carried out first, with a solution of nanoparticles (C0,p = 0.2 g/L) and secondly, with a solution of nanoparticles
and bromine. The transfer model based on fractionation of water into two phases,
mobile and immobile, MIM, correctly fits the elution curves. The retention of colloidal
particles is greater in the two media of bimodal particle size than that in the
sand, which clearly demonstrates the role of textural heterogeneity in the retention
mechanism. The increase in ionic strength produced by alimenting the columns with
colloidal particle suspension in the presence of bromide, increases retention up
to 25% in the sand. The total concentration profile of nanoparticles collected at
the end of the experiment shows that the colloidal particles are retained primarily
at the entrance of the columns. Hydrodispersive calculated parameters indicate that
flow is more heterogeneous in bimodal media compared to sand.