Aggregation of colloidal iron during estuarine mixing: Kinetics,mechanism, and seasonality |
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| Authors: | Lawrence M Mayer |
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| Institution: | Program in Oceanography and Department of Geological Sciences, Ira C. Darling Center, University of Maine at Orono, Walpole, Maine 04573, USA |
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| Abstract: | The colloid chemistry of iron and humic aggregation was studied in a series of laboratory experiments, which were related to seasonal aggregation extent data collected in a temperate estuary. Kinetically, the aggregation of iron occurs with a rapid initial reaction, finished within a few minutes, followed by an extensive, slow second reaction, which lasts for several hours. Organic carbon aggregation, however, occurs primarily in the first reaction. The first reaction is perikinetic while the second reaction is observed to be either perikinetic or orthokinetic, depending on the pore size of the filter used to clarify the suspension. The second reaction involves aggregation of small filtrable colloids (<0.5 μm) with larger aggregates formed in the first reaction, and follows pseudo-second order kinetics with respect to the filtrable iron concentration when finer filters (<0.5 μm) are used for clarification. Little or no temperature dependence is evident for the first reaction extent, while increasing temperature strongly enhances the second reaction. An activation energy of 9–11 kcal·mole?1 for the second reaction is due to a combination of transport and charge repulsion terms. Field data show a correspondingly greater aggregation extent of iron with salinity in warmer months relative to colder months. |
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