HR: 0830h
AN: B21C-0722    [PDF]
TI: Outer Sphere Adsorption: Speciation and Implications for Mineral Dissolution
AU: * Johnson, S B
EM: stephen.johnson@stanford.edu
AF: Surface and Aqueous Geochemistry Group, Department of Geological and Environmental Sciences, Stanford University, Building 320, 450 Serra Mall, Stanford, CA 94305-2115 United States
AU: Yoon, T
EM: taeyoon@pangea.stanford.edu
AF: Surface and Aqueous Geochemistry Group, Department of Geological and Environmental Sciences, Stanford University, Building 320, 450 Serra Mall, Stanford, CA 94305-2115 United States
AU: Brown, G E
EM: gordon@pangea.stanford.edu
AF: Surface and Aqueous Geochemistry Group, Department of Geological and Environmental Sciences, Stanford University, Building 320, 450 Serra Mall, Stanford, CA 94305-2115 United States
AU: Brown, G E
EM: gordon@pangea.stanford.edu
AF: Stanford Synchrotron Radiation Laboratory, SLAC, 2575 Sand Hill Road, Menlo Park, CA 94025 United States
AB: Organic substances such as low molecular weight (LMW) acids and humic substances are ubiquitous in many natural settings. In environments such as soils and sediments, organic materials commonly strongly adsorb to minerals such as metal oxyhydroxides, thereby influencing their physicochemical behavior. In particular, a number of studies undertaken in recent years have shown that organic substances that adsorb in an inner sphere fashion (ie., through a ligand exchange process, resulting in a direct organic - metal cation bond) can dramatically enhance the dissolution behavior of a range of metal oxyhydroxides. In this study, we have examined the effect of outer sphere adsorption (ie., adsorption in the absence of direct ligand - metal cation bond formation) of a simple LMW anion, maleate, on the dissolution behavior of corundum - a model metal oxyhydroxide. Combined macroscopic adsorption results, ATR-FTIR spectroscopy and dissolution data indicate that under acidic conditions, the outer sphere binding of maleate strongly inhibits mineral dissolution, presumably by blocking and protecting surface sites against attack by dissolution-enhancing species present in solution. The potential implications of these results are discussed in light of other recent spectroscopic findings, which indicate that common macromolecular organic substances such as fulvic acid also predominantly bind in an outer sphere manner on mineral oxyhydroxide surfaces.
DE: 0400 Biogeosciences
DE: 1055 Organic geochemistry
SC: Biogeosciences [B]
MN: 2003 Fall Meeting