title: Reactive transport in porous media: a comparison of model prediction with laboratory visualization.
abstract: Groundwater transport models that accurately describe spreading of nonreactive solutes in an aquifer can poorly predict concentrations of reactive solutes. The dispersive term in the advection-dispersion equation can overpredict pore-scale mixing, and thereby overpredict homogeneous chemical reaction. We quantified this experimentally by imaging instantaneous colorimetric reactions between solutions of aqueous CuSO4 and EDTA4- within a 30-cm long translucent chamber packed with cryolite sand that closely matched the optical index of refraction of water. A charge-coupled device camera was used to quantify concentrations of blue CuEDTA2- within the chamber as it was produced by mixing of the two reactants at different flow rates. We compared these experimental results with a new analytic solution for instantaneous bimolecular reaction coupled with advection and dispersion of the product and reactants. For all flow rates, the concentrations of CuEDTA2- recorded in the experiments were about 20% less than predicted by the analytic solution, thereby demonstrating that models assuming complete mixing at the pore scale can overpredict reaction during transport.
authors.affiliation: MIT/WHOI Joint Program in Oceanography, Woods Hole Oceanographic Institution, Massachusetts 02543-1050, USA.
authors.forename: Carolyn M
authors.initials: CM
authors.lastname: Gramling
authors.forename: Charles F
authors.initials: CF
authors.lastname: Harvey
authors.forename: Lucy C
authors.initials: LC
authors.lastname: Meigs
mesh_terms: D002614:Chelating Agents / Q000032:analysis / Q000737:chemistry; D019327:Copper Sulfate / Q000032:analysis / Q000737:chemistry; D004492:Edetic Acid / Q000032:analysis; D008962:Models, Theoretical; D016062:Porosity; D012989:Soil Pollutants / Q000032:analysis*; D012995:Solubility; D014873:Water Pollutants / Q000032:analysis*; D014881:Water Supply
chemical_list: D002614:Chelating Agents; D012989:Soil Pollutants; D014873:Water Pollutants; D004492:Edetic Acid; D019327:Copper Sulfate