Iron speciation in coastal rainwater : oxidation kinetics and organic complexation
- UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
- Bernard Jason Smith (Creator)
- Institution
- The University of North Carolina Wilmington (UNCW )
- Web Site: http://library.uncw.edu/
- Advisor
- Joan Willey
Abstract: The redox kinetics and organic complexation of iron were investigated in
rainwater collected from a coastal site in Wilmington, NC between September 2001 and
September 2003. A series of authentic rain samples was irradiated with simulated
sunlight to photoproduce Fe(II) and the kinetics of its reoxidation back to Fe(III) was
monitored. The oxidation of Fe(II) by hydrogen peroxide during dark storage followed
second order kinetics with an average rate constant of 0.024mM-1h-1. Using sequential
regression analysis the rate loss could be predicted accurately by the following equation
(given that H2O2 is in mM and Fe(II) is in nM units):
rate loss = -16.6 + 1.1[H2O2] + .28[Fe(II)].
In addition to studying the redox kinetics of photoproduced Fe(II) in rainwater the
importance of organic complexation on Fe speciation was also evaluated. After
approximately 2 h the concentration of photochemically produced Fe(II) decreased until
it reached levels at or near pre-irradiation values. A series of experiments demonstrated
that the photochemically produced Fe(II) rapidly returned to initial concentrations,
suggesting that essentially all the Fe(II) and most of the Fe(III) in rainwater in the
absence of sunlight occurs organically complexed. When rainwater was UV oxidized the
Fe(II) concentration declined to much lower concentrations than before irradiation,
because the organic Fe(II) complex stabilizing Fe(II) in rainwater was destroyed. A
second series of experiments demonstrated that Fe(II) present in authentic rainwater was
stabilized for up to four hours once added to seawater. When the rain was UV oxidized
prior to addition to seawater, the Fe(II) was oxidized almost immediately in the seawater
again, suggesting essentially all the Fe(II) in rain is organically complexed. In summary, the results presented in this study suggests that during the daytime
when sunlight is present there is a dynamic interconversion between inorganic Fe(II) and
Fe(III) species. Once solar irradiation is removed, there is a organically complexed form
of Fe(II) which is stabilized against oxidation. Therefore, the concentrations of Fe(II)
and Fe(III) measured in rainwater at any given time depends on the photochemical
history of the sample.
Iron speciation in coastal rainwater : oxidation kinetics and organic complexation
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Created on 1/1/2009
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Additional Information
- Publication
- Thesis
- A Thesis Submitted to the University of North Carolina at Wilmington in Partial Fulfillment Of the Requirements for the Degree of Master of Science
- Language: English
- Date: 2009
- Keywords
- Oxidation, Photochemistry, Rain-water (Water-supply)--Iron content--North Carolina--Wilmington
- Subjects
- Rain-water (Water-supply) -- Iron content -- North Carolina -- Wilmington
- Oxidation
- Photochemistry