title: Illite spatial distribution patterns dictate Cr(VI) sorption macrocapacity and macrokinetics.
abstract: This work examines the largely unexplored role of illite spatial distribution patterns in dictating the sorption of Cr(VI), a ubiquitously occurring contaminant. Flow-through experiments were carried out at 0.6, 3.0, and 15.0 m/day using columns packed with the same illite and quartz mass however with different spatial patterns and permeability contrasts. Column-scale sorption macrocapacity and macrorates were found to decrease with transport connectivity, a quantitative measure of heterogeneity characteristics. At 0.6 and 3.0 m/day, well-connected low permeability illite zones oriented in the flow-parallel direction lead to diffusion-controlled mass transport limitation for accessing sorption sites. This results in up to 1.4 order of magnitude lower macrocapacity and macrorates compared to those in minimally connected columns with well-mixed illite and quartz. At 15.0 m/day, effects of spatial heterogeneities are less significant (up to a factor of 2.8) owing to the close to chemical kinetics-controlled condition. Although the column-scale macrocapacity can reach full sorption capacity under low flow conditions, the macrorates are 10(-1) to 10(-3) of the microrates measured in well-mixed reactors. Insights gained here bridge gaps between laboratory observations and field applications and advance predictive understanding of reactive transport processes in the naturally heterogeneous subsurface.
authors.affiliation: John and Willie Leone Family Department of Energy and Mineral Engineering, ‡Earth and Environmental Systems Institute (EESI), and §EMS Energy Institute, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Li
authors.initials: L
authors.lastname: Wang
authors.forename: Li
authors.initials: L
authors.lastname: Li
mesh_terms: D000327:Adsorption; D002857:Chromium / Q000737:chemistry*; D004058:Diffusion; D007700:Kinetics; D008903:Minerals / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D008903:Minerals; D014874:Water Pollutants, Chemical; D002857:Chromium; C099089:illite; C074702:chromium hexavalent ion