Modeling Cd and Zn Sorption to Hydrous Metal Oxides

Abstract

The mobility and bioavailability of Cd and Zn in soils and sediments are affected by contaminant distribution mechanisms. One important process is sorption to hydrous aluminum, iron, and manganese oxides, which are ubiquitous in soils and sediments as both discrete particles and coatings and exhibit a high affinity for these metals. Mechanistic models are required for accurately assessing risks to populations and in the long-term management of contaminated soils and sediments. This research demonstrates intraparticle diffusion is the rate-limiting step in the sorption of Cd and Zn to microporous oxides. Furthermore, as much as 90% of the total sorption sites on the oxides reside on the micropore walls. Because longterm experiments require a lengthy period of time, predictive methods would be useful for determining surface diffusivities. Theoretically, surface diffusivities can be predicted from site activation theory, which is based on the random walk model where atoms or molecules vibrate at localized sites along the surface. Once the vibrating ion has sufficient energy, it will jump to a neighboring site. For a given metal, the associated activation energy was observed to be equivalent for all three oxides; in an effort to predict this energy, a correlation is presented between the adsorption enthalpy and the adsorbate hydrated radius. For each oxide, the Polanyi constant (R) that relates adsorption enthalpy and activation energy was equivalent for the transition metals studied.

EXAFS studies on adsorption irreversibility of Zn(II) on TiO2: Temperature dependence

“…This behavior cannot be explained by classical adsorption thermodynamics. For more complex sorption processes where multiple surface reactions and partitioning processes occur simultaneously on the heterogeneous components of a soil/sediment sample, various semiempirical models have been proposed to interpret sorption hysteresis [15][16][17][18]. However, the fundamental principle pertaining to how the reversibility of the surface adsorption can lead to different metastable equilibrium states remains unknown.…”

Parâmetros termodinâmicos da reação de adsorção de boro em solos tropicais altamente intemperizados

“…28,No. 6 mento foi conduzido 11 , enquanto outros realçaram que a vantagem da obtenção destes parâmetos, a partir de modelos, reside no fato de sua ampla aplicação, porque estes valores são derivados de constantes de equilíbrio e podem ser considerados valores padrão 12 . No entanto, os valores dos parâmetros termodinâmicos derivados de modelos provavelmente diferirão daqueles medidos diretamente por métodos calorimétricos 12 .…”

CHARACTERIZATION AND SURFACE REACTIVITY OF NATURAL AND SYNTHETIC MAGNETITES: II. ADSORPTION OF Pb(II) AND Zn(II)

“…The health risks posed to biota from heavy metals is high because they are not chemically and biologically degradable, so they will remain in the environment after disposal. Additionally, their concentrations in higher organisms may increase via the trophic chain, especially causing health problems in humans (Trivedi and Axe 2000, ATSDR 2005, USEPA 2007, Sánchez et al 2013. In order to comply with the guidelines of environmental regulatory agencies, various methodologies have been employed to remove metal ions from aqueous contaminated environments.…”