Heavy metal adsorption on iron oxide and iron oxide-coated silica ...

44(Zabinsky et al. 1995). Fits were optimized by minimizing the residuals and errors wereassessed by fitting the spectra averaged over subgroups of scans.4.8 Surface Complexation ModelingThe nonlinear least-square fitting program, FITEQL Version 4.0 (Herbelin and Westall,1999) was used for fitting parameters from titration and <strong>adsorption</strong> data. This programsolves the equilibrium model at each data point and optimizes adjustable parameters untilthe sum of the squares of the residuals (SOS/DF term in FITEQL) between the measureddata and the calculated values is minimized (Herbelin and Westall, 1999). The TLM hasthe flexibility in placing electrolyte and <strong>metal</strong> ions along the interface and therefore isselected for modeling the goethite titration and <strong>adsorption</strong> data. In distinguishing innerandouter-sphere <strong>adsorption</strong>, the TLM has been demonstrated to accurately cover a largerange of conditions (Cowan et al. 1991; Hayes and Katz, 1996; Dyer et al. 2004).Parameters calibrated from the titration data were further applied in modeling <strong>adsorption</strong>.In the following chapters, results are discussed: Chapter 5, Characterization ofIron Oxides and Silica; Chapter 6, Synthesis and Characterization of Iron Oxide-CoatedSilica; Chapter 7, Surface Complexation of Pb(II) on Amorphous Iron Oxide:Spectroscopic and Time Studies; Chapter 8, Ni(II) Complexation to Amorphous HydrousFerric Oxide: An X-ray Absorption Spectroscopy Study; Chapter 9, SurfaceComplexation Modeling of <strong>Heavy</strong> Metal Adsorption and Competition on Goethite; andChapter 10, Ni and Zn Sorption to Iron Oxide-Coated Silica.