Colloid Deposit Morphology Controls Permeability in Porous Media
Eric J. Roth
University of Colorado Denver
Processes occurring in soils and aquifers play a crucial role in contaminant remediation and carbon cycling. The flow of water through porous media like soils and aquifers, which is essential for contaminant remediation and carbon cycling, depends on the permeability, which determines how much water flows for a given hydraulic driving force. It is widely recognized that colloids (fine particles including soils, chemical precipitates, and bacteria) often control permeability, and it is known that colloid deposit morphology (the structure of deposited colloids) is a fundamental aspect of permeability, but until recently no experimental techniques were available to measure colloid deposit morphology within porous media. This research, led by the University of Colorado Denver in collaboration with Lawrence Berkeley National Laboratory, used a custom-designed experimental apparatus to perform a series of experiments using static light scattering (SLS) to characterize colloid deposit morphology within refractive index matched (RIM) porous media during flow through a column. Real time measurements of permeability, specific deposit, and deposit morphology were conducted with initially clean porous media at various ionic strengths and water velocities. Decreased permeability (i.e., increased clogging) correlated with colloid deposit morphology, specifically with lower fractal dimension and smaller radius of gyration. These observations suggest a deposition scenario in which large and uniform aggregates become deposits, which reduce porosity, lead to higher fluid shear forces, which then decompose the deposits, filling the pore space with small and dendritic fragments of aggregate. Accordingly, for the first time, observations are available to quantify the relationship between the macroscopic variables of ionic strength and water velocity and the pore-scale variables of colloid deposit morphology, which can be conceptualized as an emergent property of the system. This work paves the way for future studies that will quantify the complex feedback process between flow, chemistry, and biology in soils and aquifers.
Roth, E.J.; Gilbert, B.; Mays, D.C. (2015), Colloid deposit morphology and clogging in porous media: Fundamental insights through investigation of deposit fractal dimension, Environmental Science and Technology, 49, 12263–12270, doi:10.1021/acs.est.5b03212.
Performed by university collaborator. Did not use software/codes or user facility.
Permeability, which is crucial in groundwater remediation, depends on colloid deposit morphology. A novel application of static light scattering has allowed first-of-their-kind, real-time, in-situ measurements of deposit morphology as a fractal dimension during column filtration experiments.
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