title: Experimental determination of sorption in fractured flow systems.
abstract: Fracture "skins" are alteration zones on fracture surfaces created by a variety of biological, chemical, and physical processes. Skins increase surface area, where sorption occurs, compared to the unaltered rock matrix. This study examines the sorption of organic solutes on altered fracture surfaces in an experimental fracture-flow apparatus. Fracture skins containing abundant metal oxides, clays, and organic material from the Breathitt Formation (Kentucky, USA) were collected in a manner such that skin surface integrity was maintained. The samples were reassembled in the lab in a flow-through apparatus that simulated approximately 2.7 m of a linear fracture "conduit." A dual-tracer injection scheme was utilized with the sorbing or reactive tracer compared to a non-reactive tracer (chloride) injected simultaneously. Sorption was assessed from the ratio of the first temporal moments of the breakthrough curves and from the loss of reactive tracer mass and evaluated as a function of flow velocity and solute type. The breakthrough curves suggest dual-flow regimes in the fracture with both sorbing and non-sorbing flow fields. Significant sorption occurs for the reactive components, and sorption increased with decreasing flow rate and decreasing compound solubility. Based on moment analysis, however, there was little retardation of the center of solute mass. These data suggest that non-equilibrium sorption processes dominate and that slow desorption and boundary layer diffusion cause extensive tailing in the breakthrough curves.
authors.affiliation: Department of Geological Sciences, The University of Texas at Austin, 78712-1101, USA.
authors.forename: Mitchell D
authors.initials: MD
authors.lastname: Zimmerman
authors.forename: Philip C
authors.initials: PC
authors.lastname: Bennett
authors.forename: John M
authors.initials: JM
authors.lastname: Sharp
authors.forename: Wan-Joo
authors.initials: WJ
authors.lastname: Choi
mesh_terms: D000327:Adsorption; D000538:Aluminum Silicates / Q000737:chemistry*; D000077215:Clay; D006801:Humans; D019216:Metals, Heavy / Q000737:chemistry*; D009716:Numerical Analysis, Computer-Assisted; D010087:Oxides / Q000737:chemistry*; D014872:Water Movements; D014874:Water Pollutants, Chemical; D018508:Water Purification / Q000379:methods
chemical_list: D000538:Aluminum Silicates; D019216:Metals, Heavy; D010087:Oxides; D014874:Water Pollutants, Chemical; D000077215:Clay