Email: Williams_kristen@yahoo.com SEM image of synthetic hematite

Ferric (hydr)oxides are nearly ubiquitous in aquatic systems, occurring as fine grained sediments, coatings on primary minerals or as suspended colloids. These materials typically have high surface area and adsorption capacity making them critical in considering aqueous phase concentrations and environmental fate of trace elements in fresh and seawater systems [1, 2]. In particular the sorption of inorganic contaminants such as Pb(II), As(III)/(V), Cd(II), Zn(II) and Hg(II) to ferric (hydr)oxides is a major factor controlling aqueous concentrations and thus has important implications for the long term fate and bioavailability [3]. Metal and metalloid contaminants such as these originate from numerous natural and anthropogenic sources, and pose significant health threat via direct consumption or through bioaccumulation and biomagnification [4]. Considering the U.S. EPA's maximum contaminant level goals (MCLG) for drinking water are less than or equal to 5 ppb for most of these species, the solid phase partitioning and potential for remobilization of even trace levels are critical for water quality.

Under reducing conditions, as might be found in subsurface systems, Fe(III) (hydr)oxides may become soluble and potentially release the metals that have been scavenged under oxic conditions [5]. The presence of soluble Fe(II) may further induce the dissolution of Fe(III)-hydroxides through an abiotic catalytic mechanism [6]. Aqueous Fe(II) is highly soluble under anoxic conditions [7], yet may partition strongly to the surfaces of Fe(III)(hydr)oxides via sorption [5], potentially competing for reactive surface sites with other metals. Understanding the mechanistic details of the reductive dissolution reaction and the impact on adsorption processes is pivotal to understanding the reactivity of Fe(III)(hydr)oxides in the environment. While there has been great interest in the overall effect of the reduction of Fe(III) (hydr)oxides due to the sorption of Fe(II), the basic structural changes, mechanisms, and impact on surface reactivity have yet to be resolved. The main focus of the work proposed here is to investigate the changes in reactivity of Fe(III)(hydr)oxide substrates, specifically hematite (well crystalline α-Fe₂O₃), during and after reaction with Fe(II). This research explicitly focuses consideration on Fe(II)'s effects on Hg(II) and Cd(II) sorption. These trace metals are contaminants of concern in the state of Alaska [8, 9], and in particular, the long range atmospheric transport of Hg followed by oxidation and deposition is of particular concern due to the bioaccumulation and biomagnification in arctic ecosystem [9]. Attempts to understand the observed reactivity will employ characterization of the unreacted solid phase and sorbed metal speciation.