Surface complexation modeling of Pb(II), Cd(II) and Se(IV) onto iron hydroxides in single and bisolute systems
Year: 2006
Type: dissertation
Abstract: Many environmental problems require reliable quantitative prediction of the fate \nand transport of metal ion contaminants in surface and groundwaters. Surface \nComplexation Models (SCMs) have emerged as the most promising tools for predicting \ncontaminant ion sorption to iron (hydr)oxides. The reliability of SCMs is highly \ndependent on the ability to select appropriate surface complexation reactions and model \nparameters. This research focused on developing a strategy for developing a selfconsistent \ndatabase for the Triple Layer Model (TLM) parameters for two iron \n(hydr)oxides, ferrihydrite (HFO) and goethite (α-FeOOH). To this end, spectroscopic \ndata were used to guide the selection of surface complexation model reactions, and to the \nextent possible, theoretically based parameter estimation techniques were used to \ncharacterize the mineral surfaces throughout this work. \nThe adsorption of two divalent metals, Cd(II) and Pb(II), and one oxyanion, \nSe(IV) onto α-FeOOH and ferrihydrite was modeled in single and bi-solute systems \nusing the TLM. Selection of all surface complexes was supported by evidence from \nextended x-ray absorption fine structure spectroscopy. The fixed surface site density \nvalues based on tritium exchange experiments were used (Ns = 10.2 and 16.4 sites /nm2 \nfor ferrihydrite and goethite, respectively). Ferrihydrite was modeled using one surface \nsite while goethite was modeled with strong and weak sites, with the following \ndistribution: Nwk = 90% and Nst =10%. \nCd(II) and Pb(II) adsorption were modeled using bidentate and monodentate \nsurface complexes onto ferrihydrite. The model was able to predict the competitive \nadsorption behavior of Cd(II) and Pb(II) in bisolute systems. For the goethite system, \nCd(II) and Pb(II) adsorption was modeled using bidentate surface complexes on both \nweak and strong goethite surface sites. The TLM was able to predict the competitive \nadsorption behavior of Cd(II) and Pb(II) in bisolute systems. \nSe(IV) adsorption onto goethite was investigated in the presence of Cd(II) or \nPb(II) and was modeled using bidentate surface complexes. The TLM predicted data \nreasonably well in low and medium surface coverage single-solute systems; however, it \ndid not predict adsorption behavior for a high surface coverage adsorption edge. In \nbisolute systems, the TLM overestimated adsorption enhancement for low and medium \nsurface coverage adsorption edges. TLM predictions using lower surface site densities \nimproved the oxyanion predictions but diminished the quality of the divalent metal ion \npredictions.
Author: Adriano R. Vieira
Language: English
Subfield: Water Science and Technology
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W1804514790