Browsing by Subject "Goethite"
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Item Mercury specation during thermal remediation and in post-treatment environments(2011-12) Park, Chang Min; Liljestrand, Howard M. (Howard Michael); Katz, Lynn Ellen; Lawler, Desmond F.; Reible, Danny D.; Pope, Gary A.Mercury is a toxic metal that has been released to the environment through numerous industrial activities. It can exist in various solid, aqueous, and gaseous forms. Volatile Hg(0) is frequently present at the source of a spill where it behaves as a dense non-aqueous phase liquid (DNAPL) contaminant that can change oxidation state and speciation via chemical or biological reactions. Mercury speciation is a key factor determining the mobility, bioavailability, and toxicity of Hg in the environment. Previous research has demonstrated that In Situ Thermal Desorption (ISTD) can be used in various modes to treat soil contaminants including Hg(0). The application of ISTD and other remediation processes must incorporate potential speciation during remediation and assess mobility of any mercury remaining in the soil post-remediation. However, research examining the impact of mercury speciation on ISTD processes is limited. The goals of this research are to investigate the fate and transport of mercury in soils from the source where concentrations are expected to be high to dilute solutions associated with down gradient groundwater, lakes, and rivers. For high concentrations of mercury, equilibrium speciation has been investigated to identify potential transformations at high temperatures consistent with those applied in ISTD processes. A model has been developed that describes mercury speciation over a range of environmental conditions. At low mercury concentrations, competitive Hg(II) adsorption on the soil minerals, goethite and gibbsite, has been evaluated over a range of experimental conditions. Models describing Hg(II) adsorption and aqueous speciation have been developed to provide a tool for predicting the fate and transport of residual mercury after thermal remediation applications. The results of these studies demonstrate that ISTD is feasible, but the off-gas speciation will depend on both the applied temperatures and the soil composition and redox conditions of the site. Pure phase mercury was predicted to be vaporized at temperatures well within the range of typical ISTD processes. The adsorption of trace levels of Hg(II) remaining after ISTD was successfully modeled on goethite and gibbsite using the 1-pK CD-MUSIC model.Item Predicting ion adsorption onto the iron hydroxide goethite in single and multi-solute systems(2013-12) Mangold, Jeremiah Edward; Katz, Lynn EllenSurface complexation models (SCMs) have proven to be a useful tool in predicting ion adsorption at the mineral – water interface. In particular, previous research has shown that the Diffuse Layer Model (DLM), Constant Capacitance Model (CCM), and Triple Layer Model (TLM), are all capable of predicting ion adsorption in relatively simple single solute systems. To better simulate the environmental conditions experienced by groundwater sources present in the Earth’s subsurface, experimental adsorption studies have been conducted for more complex multi-solute systems. Under these conditions, SCMs have not proven to be reliable in consistently predicting ion adsorption behavior for the adsorbates of interest. This inability of these SCMs to predict ion adsorption for more complex, multi-solute systems is thought to stem from the variable site density (NS) values utilized in these models. In this research, a methodology was developed for characterizing mineral surface heterogeneity that allows for the different site density values predicted from crystallography, microscopic imaging, tritium exchange, surface saturation data, and surface charging data to all be explained using a single unified theory. This methodology was applied to a goethite mineral sample used in performing batch adsorption studies in single and bi-solute systems with Cd(II), Pb(II), and Se(IV). The adsorption behavior of these adsorbates onto the goethite sample was successfully predicted using the Charge Distribution Multi-Site Complexation (CD-MUSIC) Model and surface complexes consistent with spectroscopic data and computational molecular modeling simulations. A second, separate modeling study was performed using CD-MUSIC to predict Hg(II) adsorption onto different goethite samples of varying size and crystal morphology in single and multi-solute systems. In this study, site density values were predicted for the mineral samples studied utilizing a linear relationship observed for goethite between specific surface area and proton reactive site density. The CD-MUSIC model proved successful in predicting Hg(II) adsorption over all conditions studied while employing only surface complexes consistent with molecular scale analyses. In addition, a novel method for quantifying carbonate’s presence in experimental systems was developed.Item The adsorption capacity of goethite, [Greek letter a-Fe2O3H2O(Texas Tech University, 1965-05) Gibson, Everett KayNot available