Geoscience Reference
In-Depth Information
Overall, Ben-Moshe et al. (
2010
) showed that the composition of the solution
has a strong impact on the mobility of nanoparticles, both in terms of mobility and
retention in the column and in terms of elution patterns.
Large commercial use of nanoscale fullerenes (nC
60
)—an hydrophobic mole-
cule composed of 60 carbons atoms arranged in a spherical shape—suggests their
potential release to land surface. The inherent solubility of fullerene (nC
60
)in
water is very low, but stable fullerene aqueous suspensions may be formed in the
presence of commercial or natural organic compounds. Under these conditions, the
transport of fullerenes through the soil-subsurface region may occur. Some results
on the influence of environmental conditions on fullerene (nC
60
) transport in the
geochemical system are presented below.
The effects of flow conditions on the transport of fullerene (nC
60
) nanoparticles
in quartz sand were studied in column experiments by Li et al. (
2008
). Four
different fractions of Ottawa sand and two pore water velocities were tested for
fullerene breakthrough curves (Fig.
12.20
). For the lower flow rate (*m/d),
breakthrough of nC
60
aggregates was observed only in the columns packed with
20-30- and 40-50-mesh Ottawa sand (Fig.
12.20
a, b). The retention of nC
60
aggregates, expressed as the retained fullerene mass per gram of dry sand, is
related in Fig.
12.20
c, d to the distance from the column inlet. Columns packed
with coarse sands generally exhibited a slower attachment than those packed with
finer sands. A coupled mathematical model incorporating nonequilibrium attach-
ment kinetics and a maximum retention capacity is used to provide good agree-
ment between experimental and simulated results.
Additional factors that influence fullerene transport in porous media are the
electrolyte species and concentration in aqueous solutions. For example, Wang
et al. (
2008
) studied the influence of electrolyte presence in leaching water on the
retention and transport of fullerene nanoparticles in water-saturated quartz sand.
Figures
12.21
and
12.22
show fullerene concentrations in effluents, and their
retention profiles, when an initial pulse injection of fullerene into a quartz column
is leached with CaCl
2
(Fig.
12.21
) and NaCl (Fig.
12.22
) aqueous solutions. As the
electrolyte concentration increased from 1 to 100 mM, the change in nC
60
particle
diameter was minimal for the NaCl case; but in the presence of CaCl
2
, the nC
60
particle diameter increased by more than sevenfold. At low ionic strength
(3.05 mM), fullerene particles were readily transported through 40-50-mesh
quartz sand after leaching with 1.5 pore volumes of nC
60
suspension. At a tenfold
higher ionic strength and in a column packed with fine Ottawa sand (100-140
mesh), the transport of fullerene was drastically reduced due to a strong retention
in sand (higher than 95 % from the amount initially added). Based on the above
results, Wang et al. (
2008
) underlined the strong dependence of fullerene transport
on aqueous solution chemistry.
Carbon nanotubes are nanomaterials formed entirely of carbon; they are
expected to have broad industrial applications which may lead to unavoidable
releases into the soil-subsurface environment. The transport of single-walled
carbon nanotubes (SWNTs) was tested by Jaisi et al. (
2008
) in saturated laboratory
columns packed with quartz sand. SWNTs were added and then subjected to
