Date of Completion

8-18-2014

Embargo Period

8-11-2014

Advisors

Dr. Allison MacKay, Dr. Chad Johnston

Field of Study

Environmental Engineering

Degree

Master of Science

Open Access

Open Access

Abstract

Copper availability in wetland systems is controlled by strong interactions with organic matter (OM) and highly sorptive mineral precipitates, such as iron oxides. The purpose of this study is to examine copper sorption and availability by using bench scale experiments to mimic more complex geochemical systems involving iron oxide and OM. Copper, iron oxide and OM coprecipitates were prepared by varying the molar ratio of Fe:OM from 1:0 to 1:10 with a fixed Cu concentration of 1 mg/L Cu, background of 10 mM NaNO3, and a pH range of 4 to 7. Precipitate mass and Cu sorption per mass were calculated by difference based on a mass balance. We found that as the ratio of Fe:OM decreased, more Cu was removed from solution. While solids at pH lower than 5.5 showed an increase of precipitated Cu for all Fe:OM ratios, at pH higher than 5.5 and higher Fe:OM ratios, increasing Cu remained in solution. Additional samples were prepared with Cu added after precipitation (sorption) to compare the in-situ conditions (coprecipitation) to conditions typically studied in laboratories and similar trends were observed. Iron oxide-OM coprecipitates exposed to Cu at the time of precipitation produced an increase in Cu removal from solution when compared to those for which Cu was added after precipitation. Ligand extractions, ion exchange reactions and desorption experiments consistently showed a clear increase in dissolved Cu material in the coprecipitation experiments when compared to sorption for all ratios. This may indicate that Cu is more accessible when considering multicomponent systems including Cu complexed with freshly precipitated iron oxide-organic matter coprecipitates.

Major Advisor

Dr. Timothy Vadas

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