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The erosion and transport of cohesive sediment are more difficult to study than non-cohesive sediment, largely because these processes vary with the salt in the water. Clay minerals are the major components that contribute to the cohesiveness of cohesive sediment because they have significantly larger surface charges and surface area-to-volume ratio than non-cohesive sediment. The electrochemically active clay surfaces can adsorb ions on their surfaces, form an electrical double layer, and cause clay particles to aggregate or form a gel. In this chapter, we first discuss the properties of clay minerals, including the structure of clay primary particles, their surface charge and area, and their interaction with ions in water. The surface charges and surface areas of clay are several orders of magnitude larger than non-cohesive sand, thus predisposing it to interactions with salt in aqueous environments. Second, we summarize studies that reveal the role of salts, specifically salinity and sodium absorption ratio (SAR), on sediment aggregation, stability, and settling speed. An increase in salinity from 0.15 to 1.5 ppt has been shown to increase the erosion threshold of smectite clay by more than 10 times. These findings underscore the crucial role of salt in shaping cohesive sediment transport.
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This content will become publicly available on April 1, 2026
A coarse-grained model of clay colloidal aggregation and consolidation with explicit representation of the electrical double layer
Knowledge Gap: The aggregation of clay minerals in liquid water exemplifies colloidal self-assembly in nature. These negatively charged aluminosilicate platelets interact through multiple mechanisms with different sensitivities to particle shape, surface charge, aqueous chemistry, and interparticle distance and exhibit complex aggregation structures. Experiments have difficulty resolving the associated colloidal assemblages at the scale of individual particles. Conversely, all-atom molecular dynamics (MD) simulations provide detailed insight on clay colloidal interaction mechanisms, but they are limited to systems containing a few particles. Simulations: We develop a new coarse-grained (CG) model capable of representing assemblages of hundreds of clay particles with accuracy approaching that of MD simulations, at a fraction of the computational cost. Our CG model is parameterized based on MD simulations of a pair of smectite clay particles in liquid water. A distinctive feature of our model is that it explicitly represents the electrical double layer (EDL), i.e., the cloud of charge-compensating cations that surrounds the clay particles. Findings: Our model captures the simultaneous importance of long-range colloidal interactions (i.e., interactions consistent with simplified analytical models, already included in extant clay CG models) and short-range interactions such as ion correlation and surface and ion hydration effects. The resulting simulations correctly predict, at low solid-water ratios, the existence of ordered arrangements of parallel particles separated by water films with a thickness up to ~10 nm and, at high solid-water ratios, the coexistence of crystalline and osmotic swelling states, in agreement with experimental observations.
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- Award ID(s):
- 2150797
- PAR ID:
- 10574695
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Journal of Colloid and Interface Science
- Volume:
- 683
- ISSN:
- 0021-9797
- Page Range / eLocation ID:
- 1188-1196
- Subject(s) / Keyword(s):
- Molecular dynamics simulation DLVO theory clay swelling disjoining pressure adsorption electrical double layer colloid aggregation
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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