Experimental Studies of Geochemical Reactions that Affect the Mobility of Metals and Nanoparticles of Environmental Interest

Adsorption and adhesion of metals and engineered nanoparticles onto geosorbents can have a significant impact on their fate and transport. Interactions with fixed mineral and bacterial surfaces may remove contaminants from solution and decrease their mobility, although removal may be selective. Conversely, when the surfaces themselves are mobile as colloids, the transport of contaminants may be enhanced by adsorption and adhesion reactions. Natural organic matter (NOM), a complex mixture of organic molecules, is widespread in environmental systems and can influence adsorption and adhesion through aqueous and surface complexation reactions. This research focuses on the interactions of NOM, cadmium (Cd(II)), and nanoparticles with geosorbents, as well as the potential reactivity of bacterial exudates, under a range of aqueous conditions. Three experimental studies will be described: 1) flow-through column experiments to study the effects of NOM on Cd(II) mobility and of Cd(II) on NOM sorptive fractionation in various types of mineral sands; 2) an investigation of influence of pH, nanoparticle size, and nanoparticle concentration on the adhesion of titanium dioxide nanoparticles to silica and iron-coated silica grains; and 3) the use of potentiometric titrations and chemical equilibrium modeling to evaluate the proton binding of bacterial exudates collected from Gram-positive (Bacillus subtilis) and Gram-negative (Shewanella oneidensis) bacterial species. From the results of these laboratory studies, it is possible to better understand contaminant mobility in realistic geologic systems.