Retention Site Contribution towards Silver Particle Immobilization in Porous Media

Janis E. Patiño, Francisco Pérez Reche, Verónica L. Morales* (Corresponding Author)

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

This work investigates the role that pore structure plays in colloid retention across scales with a novel methodology based on image analysis. Experiments were designed to quantify–with robust statistics–the contribution from commonly proposed retention sites toward colloid immobilization. Specific retention sites include solid-water interface, air-water in terface, air-water-solid triple point, grain-to-grain contacts, and thin films. Variable conditions for pore-water content, velocity, and chemistry were testedin a model glass bead
porous medium with silver microspheres. Concentration signals from effluent breakthrough and spatial profiles of retained particles from micro X-ray Computed Tomography were used to compute mass balances and enumerate pore-scale regions of interest in three dimensions. At the Darcy-scale, retained colloids follow non-monotonic deposition profiles, which implicates effects from flow-stagnation zones. The spatial distribution of immobilized colloids along the porous medium depth was analyzed by retention site, reveal26 ing depth-independent partitioning of colloids. At the pore-scale, dominance and over all saturation of all retention sites considered indicated that the solid-water interface and wedge-shaped regions associated with flow-stagnation (grain-to-grain contacts in satu rated and air-water-solid triple points in unsaturated conditions) are the greatest contributors toward retention under the tested conditions. At the interface-scale, xDLVO energy profiles were in agreement with pore-scale observations. Our calculations suggest favorable interactions for colloids and solid-water interfaces and for weak flocculation (e.g.,at flow-stagnation zones), but unfavorable interactions between colloids and air-water
interfaces. Overall, we demonstrate that pore-structure plays a critical role in colloid immobilization and that Darcy-, pore- and interface-scales are consistent when the pore structure is taken into account.
Original languageEnglish
Article numbere2021WR031807
Number of pages15
JournalWater Resources Research
Volume58
Issue number5
Early online date30 Apr 2022
DOIs
Publication statusPublished - 1 May 2022

Keywords

  • colloid
  • filtration
  • interfaces
  • pore structure
  • upscaling
  • stagnation zones

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