Abstract
Fractures are likely to be favorable carriers for colloids and
nanoparticles due to their large aperture, enabling relatively high flow
velocity and smaller tortuosity of the flow path in comparison to flow
through the surrounding rock matrix. Here, we will briefly summarize
years of research concerning colloid and colloid-facilitated transport
in fractures. We will discuss: (1) processes in the unsaturated zone,
where fractures are exposed to wetting and drying cycles which enhance
the release and mobilization of colloids from fracture surfaces and
filling materials; (2) the relationship between colloid properties and
mobility within saturated systems; (3) the impact of groundwater
salinity on colloid transport; (4) colloid facilitated transport of Pb,
Cs , Cr and NZVI's; and (5) finally, large scale field experiments
examining the mobility of colloids in fractures. Our results
demonstrate that wetting and drying cycles in fractures crossing the
upper vadose zone result in release and mobilization of fine particles.
Experiments carried out in saturated fractures indicate high recovery of
large microspheres (0.2 and 1 micron) and lower recovery of the small
spheres (0.02 micron). It was observed that clay particles exhibit lower
recoveries than the microspheres (50% and 90%, respectively) due to
their higher density (2.65 vs. 1.05 g/cm3). In all cases, arrival times
of colloids were earlier than that of the reference species, bromide or
uranine. It was found that colloid-facilitated transport played a major
role in the migration of lead, cerium and cesium through fractures. In
the case of cerium, intrinsic colloids formed through the precipitation
of Ce2(CO3)3 resulted in cerium's increased mobility. Work on NZVI
particle transport through fractures showed that the particles' mobility
was linearly correlated with gravitational stability. In conclusion, it
was observed that in many cases, fractures are favorable carriers for
colloids and facilitate colloid-associated transport of contaminants
with high affinity to the solid matrix. It was found that even on a
large scale, fractures may enable massive transport of colloidal matter.
However, each colloid and contaminant should be explored under relevant
geochemical and physical conditions to best predict environmental
behavior.
| Original language | English GB |
|---|---|
| Pages (from-to) | 2224 |
| Journal | Geophysical Research Abstracts |
| State | Published - 1 Apr 2018 |
| Event | American Geophysical Union (AGU) Fall Meeting 2018 - Walter E. Washington Convention Center, Washington, United States Duration: 10 Dec 2018 → 14 Dec 2018 https://www.rff.org/events/speeches-and-presentations/2018-american-geophysical-union-agu-fall-meeting/ |