Doctor of Philosophy (PhD)
Plant, Environmental Management and Soil Sciences
The bioavailability and fate of Zinc (Zn) in soils is influenced by reactions occurring at the water-mineral interface. Understanding Zn interaction with mineral surfaces is essential to the understanding of Zn fate and toxicity. In this study, adsorption experiments investigated the impact of ligands and pH on the adsorption of Zn to mineral surfaces. X-Ray Absorption Fine Structure Spectroscopy (XAFS) was used to elucidate the adsorption mechanisms of Zn to mineral surfaces as impacted by ligands. Impact of ligands on Zn adsorption was dependent on mineral type and pH of the system. XAFS analysis showed that adsorption mechanisms of Zn were impacted by pH and ligand presence. In the ferrihydrite system, Zn adsorption was enhanced in presence of citrate and phosphate (PO4), reduced in presence desferrioxamine (DFO-B), and reduced in presence of humic acid (HA) at pH>6.0. XAFS analysis showed that Zn formed strong linkages with high affinity edge sites of ferrihydrite in the control and in presence of enhancing ligands (citrate and PO4), whereas formed weaker, low affinity linkages in presence of supressing ligands (DFO-B and HA). From an environmental perspective, Zn was more likely to be desorbed from the ferrihydrite surface in the presence HA and DFO-B. In the kaolinite system, Zn adsorption was reduced in presence of citrate and DFO-B, and increased in presence of HA. Zn formed inner sphere complexes at pH 5.5 in the control and in presence of ligands. At pH 7.5, a Zn-Al layered double hydroxide was formed in the control, that was absent in presence of any ligand, suggesting that ligands suppress the formation of Zn-Al LDH in kaolinite. In the mixed ferrihydrite-gibbsite system, Zn adsorption was enhanced in presence of all ligands, excluding DFO-B. Adsorption mechanisms of Zn to ferrihydrite were unaffected by ligand presence. The impact of organic matter (OM) degradation on heavy metal distribution in sewage sludge was investigated. Cu, Pb and As were bond with the OM fraction of sludge, whereas Zn was bond to Fe/Mn oxide fraction. OM degradation increased mobility and bioavailability of Zn and Cu, whereas it had less impact on Pb and As.
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Stietiya, Mohammed Hashem, "Sorption mechanisms of zinc in different clay minerals and soil systems as influenced by various natural ligands" (2010). LSU Doctoral Dissertations. 3592.
Wang, Jim J.