title: Kinetic metal release from competing processes in aquifers.
abstract: Understanding groundwater time scales wherein kinetic metal-desorption and mineral-dissolution are important mechanisms is essential for realistic modeling of metal release. In this study, release rate constants were compiled and the Damköhler number was applied to calculate residence times where kinetic formulations are relevant. Desorption rate constants were compiled for arsenic, barium, cadmium, copper, lead, mercury, nickel, and zinc, and span 6 orders of magnitude, while mineral-dissolution rate constants compiled for calcite, kaolinite, smectite, anorthite, albite, K-feldspar, muscovite, quartz, goethite, and galena ranged over 13 orders of magnitude. This Damköhler analysis demonstrated that metal-desorption kinetics are potentially influential at residence times up to about two years, depending on the metal and groundwater conditions. Kinetic mineral-dissolution should be considered for nearly all residence times relevant to groundwater modeling, provided the rate, solubility, and availability of the mineral generates a non-negligible concentration. Geochemical models of competitive desorption and dissolution for an illustrative metal demonstrate total metal concentrations may be sensitive to dissolution rate variations despite the predominance of release from desorption. Ultimately, this analysis provides constraints on relevant processes for incorporation into transport models.
authors.affiliation: Civil and Environmental Engineering Department, Hydrologic Science and Engineering Program, Water Modeling Center Colorado School of Mines 1500 Illinois Street Golden, Colorado 80401, United States.
authors.forename: Lindsay A
authors.initials: LA
authors.lastname: Bearup
authors.forename: Alexis K
authors.initials: AK
authors.lastname: Navarre-Sitchler
authors.forename: Reed M
authors.initials: RM
authors.lastname: Maxwell
authors.forename: John E
authors.initials: JE
authors.lastname: McCray
mesh_terms: D060587:Groundwater; D007700:Kinetics; D008670:Metals / Q000737:chemistry*; D008962:Models, Theoretical; D012995:Solubility
chemical_list: D008670:Metals