Flux of ferrous iron (FeII) to the estuarine environment, whether from bottom sediments or via groundwater seepage, has been identified as a potentially important source of iron required for the development and sustenance of nuisance blooms of the toxic cyanobacteria Lyngbya majuscula in Moreton Bay, Queensland. However the rapid oxidation of FeII in seawater imparts importance to the resultant form of ferric iron (FeIII). Oxidation of FeII in the presence of natural organic matter (NOM) results in a mixture of FeIII-NOM complex and amorphous ferric oxides (AFO). The fate of these oxidation products has implications for the supply of iron to L. majuscula where transformations over time scales of hours are likely to be important. In this thesis the process of oxidation of FeII in seawater in the presence of NOM and the subsequent transformations of the products of oxidation are investigated. UV and visible spectroscopic techniques were used to monitor the production of organically complexed FeIII for both NOM and a model organic compound. Kinetic modelling of data facilitated the examination of key reactions, especially those involving AFO. Controls on the reactivity and aging of AFO were investigated using two different dissolution reactions to measure reactivity. Light scattering techniques were used to probe the structure of AFO and X-ray absorption spectroscopy was used to examine the coordination environment of Fe centres within AFO. Analysis of a kinetic model of iron transformations parameterised using the best available knowledge revealed large uncertainty surrounding the role of ligand classes in complex formation and dissociation and the role of AFO in both formation of oxidation products and the subsequent decay of organically complexed FeIII. Laboratory studies demonstrated that, within a wide range of initial concentrations, unstable mixtures of FeIII-NOM and AFO are produced from the oxidation of FeII in seawater containing NOM and that the organic complexes immediately commence transformation to AFO. Simulation using numerical kinetic modelling of the processes investigated indicated that AFO has a significant role in the processes of formation of oxidation products and dissociation of organically complexed FeIII. The rapid aging that AFO was recognised to undergo was successfully incorporated into the model though whether the aging was due toeither 1) increased coordination of Fe centres or 2) decreased Fe centre accessibility due to aggregation could not be ascertained from the model results. However, together with information regarding the coordination environment of the Fe centres and the particle and fractal structure of the aggregates, aggregation was considered most likely to be the factor responsible for the observed and modelled decreases in AFO reactivity.
| Identifer | oai:union.ndltd.org:ADTP/281971 |
| Date | January 2009 |
| Creators | Bligh, Mark William, Civil & Environmental Engineering, Faculty of Engineering, UNSW |
| Publisher | Awarded By:University of New South Wales. Civil & Environmental Engineering |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://unsworks.unsw.edu.au/copyright, http://unsworks.unsw.edu.au/copyright |
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