Redox transformation of aqueous contaminants mediated by interfacial iron species

Iron-containing mineral surfaces are of tnterest to environmental researchers because of their prevalent presence and significant activity in mediating contaminant transformation in the natural environment and engineered treatment systems. Despite the extensive research on bulk and single-phased iron oxides, the molecular iron species deposited on common mineral colloids, which is referred to as interfacial iron species in this dissertation work, have not yet been systematically examined for their reactivity in different aquatic systems. The overall objective of this dissertation is to examine the surface chemistry and reactivity of a range of iron-containing surfaces in catalyzing redox transformation of aqueous contaminants. This is achieved through investigations of several reactions systems: 1) the deposition of interfacial iron species on silica and alumina colloids and their activation of peroxide for oxidative transformation of organic carbon, 2) the interactions between arsenic and surface iron species arising during coagulation treatment and the role of the latter in catalyzing arsenite oxidation, 3) the activation of H2O2 and peroxydisulfate (persulfate) by two types of synthetic iron-containing catalysts for reactive oxidants generation. Multiple experimental methods were used in this dissertation work, including aqueous experimentation, spectrometric determination of aqueous constituents and advanced spectroscopic techniques including X-ray Electron Spectroscopy, Transmission Electron Microscopy. Results of this work provide several contributions. The study on activation of peroxide underlines the importance of interfacial iron species instead of iron oxide particles in contributing to catalytic oxidation of contaminants at the solid-water interface. The varying behaviors of Fe impregnated on the three types of mineral colloids reveal a strong impact of the support materials on iron species’ reactivity. Furthermore, coagulation process enhanced with Fe(II) or H2O2 amendment has pointed to the feasibility of tapping into the reactivity of in situ produced iron colloids as catalytic surfaces for more effective sequestration of pollutants such as aresenite. Since traditional coagulation treatment is widely applied in drinking water treatment plants, oxidative coagulation may provide a feasible option to small municipalities and rural communities to achieve arsenic compliance. Last but not the least, the investigations over the reactivity of synthetic iron-based materials conclude that iron-bearing xerogels represent a viable candidate of environmentally benign catalysts for peroxide-based oxidative treatment, while the incorporation of copper into spinel ferrite structure offers good catalytic activity in persulfate system.