Title page for ETD etd-02232006-113157

Type of Document Master's Thesis
Author Garman, Stephanie Michelle
Author's Email Address sgarman@vt.edu
URN etd-02232006-113157
Title Desorption Kinetics of Lead from Goethite: Effect of Mixing and Sorption Period
Degree Master of Science
Department Crop and Soil Environmental Sciences
Advisory Committee
Advisor Name Title
Eick, Matthew J. Committee Chair
Daniels, Walter Lee Committee Member
Zelazny, Lucian W. Committee Member
  • Miscible Displacement
  • Desorption
  • Lead
Date of Defense 2006-02-10
Availability restricted
In natural systems, the solution concentration and hence, potential bioavailability of trace metals is primarily controlled by adsorption-desorption reactions at the mineral-water interface. While many studies have been conducted to understand the adsorption of trace metals to soil minerals, less is known about long-term adsorption/desorption processes. In this study, we examined the influence of mixing and sorption period on the desorption of lead from goethite. Lead sorption was rapid and essentially complete in 1 h, with no change in the quantity of lead adsorbed over the 6 month sorption period. Desorption of lead was slower than the adsorption reaction and was best modeled by two first order equations. At all sorption densities, the desorption of lead followed the order Short-term (24 h) > Long-term non-stirred (6 months) > Long-term stirred (6 months). However, statistical analysis indicated that these differences were not statistically significant. Furthermore, the desorption rate coefficients were very similar for all the experiments indicating that there was no significant residence time effect in this study. However, a sample from a previous study that was allowed to age 5 years and then analyzed by the desorption procedure did have statistically significant differences between the long-term (5 years) and the short-term (5 months). These results suggest that longer adsorption periods, perhaps a number of years, may be necessary to determine if residence time effects are an artifact of the experimental conditions or truly the length of the adsorption period.

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