Molecular Models of Radionuclide Interaction with Soil Minerals

Cygan, Randall T.

doi:10.2136/sssaspecpub59.c5

Cited by 2 publications

(1 citation statement)

References 94 publications

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“…Al-, Mn-and Fe-oxyhydroxides have variable charged surfaces (amphoteric) that acquire a positive charge density when the pH is more acidic than the mineral's point of zero net charge density [39,40]. Uranyl ions, along with its hydroxyl monomers and hydroxyl polymers, will participate in adsorption reactions with phyllosilicates and Mn-and Fe-oxyhydroxides [41][42][43][44][45][46][47][48][49]. The transport of U-bearing colloids by wind and water erosion is an important source of U transport from impacted sites.…”

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Chemical Thermodynamics of Uranium in the Soil Environment

Aide¹

2018

Uranium - Safety, Resources, Separation and Thermodynamic Calculation

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Uranium is present in the soil environment because of human activity, including the usage of U-bearing phosphorus fertilizers. In oxic and many suboxic soil environments, U(VI) is the dominant uranium valence species. With pH, pe (Eh), the partial pressure of CO 2 , the mineralogy of the adsorbing surfaces and the uranium concentration as the key master variables, U(VI) will predictably participate in hydrolysis, ionpairing, complexation, ion-exchange, mineral precipitation and adsorption reactions. An extensive listing of thermochemical data is currently available for detailed simulations to assist with model setup, data interpretation and system understanding. In this chapter, simulations of U(VI) hydrolysis with variable pCO 2 activities, U(IV) and U(VI) precipitation, U(VI) reduction and U(VI) complexation with carbonate and phosphate assemblages illustrate the usefulness and applicability of simulations in data analysis and experimental design.Uranium is the third element in the actinide series having an atomic number of 92 and an electronic configuration of [Rn] 5f 3 6d 1 7s 2 . The 5f orbitals are less effective in penetrating the inner core electrons than the 4f orbitals (lanthanide series), thus permitting more favored covalent bonding character [1]. Uranium(IV) and uranium(VI) have ionic radii of 89 and 73 pm, respectively. The two, more abundant, long-lived isotopes of uranium are 235 U 92 and 238 U 92 . The naturally occurring mass abundances of uranium isotopes are 234 U (0.0057%), 235 U (0.71%) and 238 U (99.284%). 235 U is fissile, whereas 238 U in a breeder reactor will yield fissile 239 Pu [2].Uranium decay is an isotope function, with (i) 238 U92 decaying by α-emission to 234 Th 90 (halflife of 4.45 × 10 9 years) and then by two successive β-emissions (half-life of 24.1 days and halflife of 1.18 minutes) to yield 234 U. 234 U will undergo α-emission (half-life of 2.45 × 10 5 ) to yield 230 Th 90 , whereas 235 U decaying by α-emission to yield 231 Th (half-life of 7.04 × 10 8 years) and later in the decay sequence to yield 227 Th [2].

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confidence: 99%

Chemical Thermodynamics of Uranium in the Soil Environment

Aide¹

2018

Uranium - Safety, Resources, Separation and Thermodynamic Calculation

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Linking the Geosciences to Emerging Bio-Engineering Technologies

Cygan¹,

Ho²,

Weiss³

2002

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Is application of Geosciences research at Sandia National Laboratories to biological and human health systems beneficial to the lab's biotechnology efforts? This LDRD project was funded to answer that question for three application areas: biochemistry, bioengineering, and human health. The biochemistry section includes modeling for protein folding and improved drug delivery substrates. For those molecular simulations, a hybrid energy forcefield was developed to model the conformation of an oligopeptide within the clay interlayer. Results demonstrate that the nonbonded interactions are especially important in understanding the control of the structure and function of proteins as modified by inorganic substrates, and that the protein structure may be denatured by the clay surface. More sophisticated molecular simulations involving waters of solvation for the protein, hydrated clay interlayers, and different charged distributions in the clay substrates are recommended for future research. The bioengineering section focuses on drug delivery and hazardous chemical absorption through the skin. Percutaneous absorption of chemicals was developed using a probabilistic, multiphase, heterogeneous model of the skin. Penetration routes through the skin included intercellular diffusion through the stratum corneum, diffusion through aqueous-phase sweat ducts, and diffusion through oil-phase hair follicles. Mass fluxes were calculated for varying lengths of time, and sensitivity analyses showed that the aqueous solubility limit, thickness of the stratum corneum, and aqueous molecular diffusion coefficient were important input parameters. Complex flow and transport models used for enhanced oil recovery, geothermal energy production, and subsurface contaminant migration could be used to further model percutaneous absorption. The human health section includes a review of the geophysical imaging methods that have been used for imaging the interior of the human body, including electrical impedance tomography and magnetic induction tomography.Accurate 3D interpretations of surface or near surface voltage/current or electromagnetic field measurements are dependent upon the inversion algorithms used. EIT impedance inversion is computationally less challenging than EM induction inversion, but rapid and resource-efficient solutions are being developed for geophysical applications. Details of this report can be found at

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Molecular Models of Radionuclide Interaction with Soil Minerals

Cited by 2 publications

References 94 publications

Chemical Thermodynamics of Uranium in the Soil Environment

Chemical Thermodynamics of Uranium in the Soil Environment

Linking the Geosciences to Emerging Bio-Engineering Technologies

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