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Colloid population heterogeneity drives hyperexponential deviation from classic filtration theory
Meiping Tong1, William P Johnson
1Department of Geology and Geophysics, The University of Utah, Salt Lake City, Utah 84112, USA.
Environmental Science & Technology
|February 22, 2007
Summary
Colloid deposition in porous media showed hyperexponential retention profiles, deviating from standard filtration theory. This deviation was driven by colloid population heterogeneity, not secondary energy minima.
Area of Science:
- Colloid and surface science
- Environmental engineering
- Geochemistry
Background:
- Understanding colloid transport in porous media is crucial for environmental remediation and resource management.
- Classic filtration theory often fails to predict colloid retention accurately, especially under varying flow conditions.
- Polystyrene latex microspheres are commonly used model colloids in environmental studies.
Purpose of the Study:
- To investigate the deposition behavior of carboxylate-modified polystyrene latex microspheres in packed porous media.
- To determine the influence of microsphere size and pore fluid velocity on colloid retention.
- To elucidate the mechanisms driving deviations from traditional filtration theory.
Main Methods:
- Experiments were conducted using packed columns of soda-lime glass beads.
- Six sizes of carboxylate-modified polystyrene latex microspheres (0.1-2.0 µm) were used.
- Pore fluid velocities ranged from 4-8 m/day, simulating environmentally relevant conditions.
- Columns in series were employed to analyze colloid population heterogeneity.
- Ionic strength manipulation was used to probe retention mechanisms.
Main Results:
- Hyperexponential retention profiles were observed for all microsphere sizes and tested velocities.
- Colloid population heterogeneity was identified as the primary driver for deviations from filtration theory.
- A significant fraction of retained colloids was released when ionic strength was lowered.
- Retention was primarily attributed to secondary energy minima, but not exclusively.
- No preferential re-entrainment of secondary minimum-associated colloids occurred near the column inlet.
Conclusions:
- Colloid population heterogeneity significantly impacts deposition behavior in porous media, leading to hyperexponential retention.
- While secondary energy minima play a role in colloid retention, they do not fully explain the observed hyperexponential deviation.
- Further research is needed to fully understand the complex interplay of factors governing colloid transport and deposition in environmental systems.
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