title: Transport of silica colloids through unsaturated porous media: experimental results and model comparisons.
abstract: We present results on the migration of silica colloids through laboratory columns packed with partially saturated quartz sand. The transport of the silica colloids responds to changes in the steady-state volumetric moisture content (theta) and for low theta depends on the wetting history of the sand pack prior to colloid injection. A mathematical model that incorporates a first-order rate law to simulate film straining and a second-order rate law to simulate partitioning at air-water interfaces closely describes colloid transport and mass transfer over the range of experimental conditions tested. The mass-transfer parameters of the model are sensitive to changes in both the level of water saturation and the flow rate. A semiempirical expression, based on a modification of film-straining theory, accounts for the observed variation in the first-order rate coefficient with changes in theta and average porewater velocity. Our work indicates that the presence of the air phase substantially influences porewater concentrations of mineral colloids in water-unsaturated media and that the kinetics of particle removal attributed to air-water boundaries reflects the contribution of multiple mass-transfer mechanisms.
authors.affiliation: School of Forestry and Environmental Studies, Yale University, Greeley Laboratory, New Haven, Connecticut 06511, USA.
authors.forename: John J
authors.initials: JJ
authors.lastname: Lenhart
authors.forename: James E
authors.initials: JE
authors.lastname: Saiers
mesh_terms: D003102:Colloids / Q000737:chemistry*; D019015:Geologic Sediments / Q000737:chemistry; D007700:Kinetics; D008962:Models, Theoretical; D016062:Porosity; D011791:Quartz / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry*; D014872:Water Movements; D014873:Water Pollutants
chemical_list: D003102:Colloids; D014873:Water Pollutants; D011791:Quartz; D012822:Silicon Dioxide