title: Impact of gravity, collector surface roughness and fracture orientation on colloid retention kinetics in an artificial fracture.
abstract: The interaction of monodisperse fluorescent carboxylated polystyrene colloids (25nm and 1000nm diameter) with a cut granodiorite surface (Grimsel granodiorite; Switzerland) and with acrylic glass is investigated both experimentally and numerically. Colloid transport experiments are conducted in a parallel plate type fracture flow cell with an aperture of 0.75mm at pH5 under low ionic strength (1mM NaCl) and under laminar flow (7mL/h) conditions. The study focuses on the effect of residence time, colloid size, collector material and fracture orientation on colloid retention. Long colloid residence times are achieved by stop-flow experiments. Using atomic force microscopy and, more specifically, the colloid probe technique surface roughness and force distance information of the collector material (granodiorite or acrylic glass) as a function of probe size (cantilever) are obtained. The experiments are modeled using COMSOL Multiphysics® (2-D numerical simulations). The experimental and the modeled results lead to the conclusion that large colloids (1000nm diameter) undergo sedimentation and deposition on the surface during stop-flow. Collector interaction is not affected by the surface roughness variation. Contrariwise, for the investigated 25nm colloids sedimentation does not play a role under the experimental conditions and collector interaction is triggered by surface inhomogeneities such as surface roughness.
authors.affiliation: Karlsruhe Institute of Technology (KIT), Institute for Nuclear Waste Disposal (INE), P.O. Box 3640, 76021 Karlsruhe, Germany. Electronic address: madeleine.stoll@kit.edu.
authors.forename: M
authors.initials: M
authors.lastname: Stoll
authors.affiliation: Karlsruhe Institute of Technology (KIT), Institute for Nuclear Waste Disposal (INE), P.O. Box 3640, 76021 Karlsruhe, Germany.
authors.forename: F M
authors.initials: FM
authors.lastname: Huber
authors.affiliation: Karlsruhe Institute of Technology (KIT), Institute for Nuclear Waste Disposal (INE), P.O. Box 3640, 76021 Karlsruhe, Germany; National Institute of Technology, Tadepalligudem, Andhra Pradesh, 534101, India.
authors.forename: G K
authors.initials: GK
authors.lastname: Darbha
authors.affiliation: Karlsruhe Institute of Technology (KIT), Institute for Nuclear Waste Disposal (INE), P.O. Box 3640, 76021 Karlsruhe, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Schill
authors.affiliation: Karlsruhe Institute of Technology (KIT), Institute for Nuclear Waste Disposal (INE), P.O. Box 3640, 76021 Karlsruhe, Germany; Karlsruhe Institute of Technology (KIT), Institute of Applied Geosciences (AGW), Environmental Geology, Karlsruhe, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Schäfer
keywords: Carboxylated latex spheres; Colloid transport; Fracture; Modeling; Sedimentation; Surface roughness