Geochemical Controls on Iron Biomineralization
All of the research projectes in our lab incorporate aspects dedicated to defining biomineralization products and pathways. The mineralization of metals, in most cases, involves redox transformations, including those discussed in the three other research areas.
We also have a number of other projects specifically investigating the geochemical controls on mineralization of Mn and Fe via abiotic and biotic processes. One of these includes defining the mineralogical constraints on reduction of Fe(III) (hydr)oxides and subsequent biomineralization by Fe(III)-reducing microbes. Iron oxides are considered one of the most important sinks for (in)organic contaminants and nutrients within soils, sediments, and waters. As a consequence of their high surface area and density of reactive surface sites, Fe(III) oxides may sorb numerous organics (e.g. pesticides, PAHs), nutrients (e.g. phosphate), and metals (e.g. transition metals, U, Sr, Tc). Consequently, the dissolution of metal-laden Fe(III) oxide phases poses a serious threat to water quality should anaerobiosis occur. In contrast, the reduction of Fe(III) oxides may also be coupled to the degradation and/or sequestration of contaminants within natural and engineered systems. Previous studies have revealed that microbial reduction of various Fe(III) oxides is transient, having a diminished reductive capacity over time. Iron oxides are mineralogically diverse, with the most studied, and most utilized, phase being ferrihydrite. While ferrihydrite is considered the most ‘bioavailable’ Fe(III) oxide for microbial reduction, we have previously observed that, under some conditions, more recalcitrant phases, such as goethite, can be more reactive. Recent data suggests that the compromised reactivity of Fe(III) phases for microbial reduction is the presence of co-precipitating ions, such as Al. Thus, we are investigating the role of sorbed and co-precipitated ions on the reactivity and biomineralization pathways of synthetic and natural Fe(III) (hydr)oxides. Our aim is to continue defining our conceptual model of biotic and abiotic controls on the competing and complimentary biomineralization pathways of Fe and Mn within environmental systems.