title: Light reflection visualization to determine solute diffusion into clays.
abstract: Light reflection visualization (LRV) experiments were performed to investigate solute diffusion in low-permeability porous media using a well-controlled two-dimensional flow chamber with a domain composed of two layers (one sand and one clay). Two different dye tracers (Brilliant Blue FCF and Ponceau 4R) and clay domains (kaolinite and montmorillonite) were used. The images obtained through the LRV technique were processed to monitor two-dimensional concentration distributions in the low-permeability zone by applying calibration curves that related light intensity to equilibrium concentrations for each dye tracer in the clay. One dimensional experimentally-measured LRV concentration profiles in the clay were found to be in very good agreement with those predicted from a one-dimensional analytical solution, with coefficient of efficiency values that exceeded 0.97. The retardation factors (R) for both dyes were relatively large, leading to slow diffusive penetration into the clays. At a relative concentration C/C0=0.1, Brilliant Blue FCF in kaolinite (R=11) diffused approximately 10 mm after 21 days of source loading, and Ponceau 4R in montmorillonite (R=7) diffused approximately 12 mm after 23 days of source loading. The LRV experimentally-measured two-dimensional concentration profiles in the clay were also well described by a simple analytical solution. The results from this study demonstrate that the LRV approach is an attractive non-invasive tool to investigate the concentration distribution of dye tracers in clays in laboratory experiments.
authors.affiliation: Soil and Water Science Department, University of Florida, Gainesville, FL 32611, USA.
authors.forename: Minjune
authors.initials: M
authors.lastname: Yang
authors.affiliation: Department of Environmental Engineering Sciences, University of Florida, Gainesville, FL 32611, USA.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Annable
authors.affiliation: Soil and Water Science Department, University of Florida, Gainesville, FL 32611, USA. Electronic address: Jawitz@ufl.edu.
authors.forename: James W
authors.initials: JW
authors.lastname: Jawitz
mesh_terms: D001391:Azo Compounds / Q000737:chemistry; D001546:Bentonite / Q000737:chemistry*; D001557:Benzenesulfonates / Q000737:chemistry; D004396:Coloring Agents / Q000737:chemistry*; D004058:Diffusion; D004784:Environmental Monitoring / Q000295:instrumentation / Q000379:methods*; D007616:Kaolin / Q000737:chemistry*; D008027:Light; D009282:Naphthalenesulfonates; D010539:Permeability; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D001391:Azo Compounds; D001557:Benzenesulfonates; D004396:Coloring Agents; D009282:Naphthalenesulfonates; D014874:Water Pollutants, Chemical; D001546:Bentonite; D007616:Kaolin; C006796:brilliant blue; C576297:ponceau 4R
keywords: Argillic; Back-diffusion; Diffusion; Groundwater; Tracer