Scaling of adsorption reactions: U(VI) experiments and modeling

Loganathan, Vijay A.; Barnett, Mark O.; Clement, T. Prabhakar; Kanel, Sushil R.

doi:10.1016/j.apgeochem.2009.07.016

Cited by 20 publications

(5 citation statements)

References 40 publications

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“…The Fe method was able to independently predict the pH where q/q max = 0.5 within 0.2 pH units and the q max within a factor of ∼ 1.25. Although subsequent studies had shown that adsorption on a per m 2 basis was an even better predictor of U(VI) adsorption to goethite-coated sand [31], we observed the opposite for Th(IV). On a per m 2 basis, the goethite data predicted an SRS adsorption of maximum of ∼ 1.5 μmol m −2 , approximately twice the q max actually measured on the SRS sand.…”

Section: Discussioncontrasting

confidence: 53%

“…The fact that the measured q max for the SRS sand was greater than predicted on the basis of the goethite data alone undoubtedly reflects adsorption contributions from minerals in addition to goethite (e.g., Al oxyhydroxides, clays, etc.). Although as noted above, Barnett et al [38] has shown that Fe content was a good predictor of U(VI) adsorption to heterogeneous Fe-containing geomedia, Loganathan et al [31] subsequently demonstrated that total surface area was an even better predictor than Fe content of U(VI) adsorption to goethite-coated sand. However, in comparing data sets normalized to surface area, Hartzog et al [39] has shown that the ratios of adsorbate to total surface area between the systems being compared should be as close as possible.…”

Section: Thorium Adsorption To Geomediamentioning

confidence: 95%

“…Goethite was identified as the second most predominant mineral and the principal Fe phase. Pure crystalline goethite was synthesized using the method described by Loganathan et al [31]. The mineralogy was confirmed by x-ray diffraction, and the surface area was measured as 31.75 m 2 g −1 using multipoint N 2 (g) BET.…”

Section: Methodsmentioning

confidence: 99%

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Adsorption of tetravalent thorium by geomedia

Melson¹,

Haliena²,

Kaplan³

et al. 2012

Radiochimica Acta

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We measured the pH-dependent adsorption of Th(IV), an analogue for Pu(IV) and other tetravalent actinides, to two geomedia: goethite (α-FeOOH(s)) and a heterogeneous Fe-containing sand from the southeastern USA. The goal was to examine whether or not the Th(IV)-goethite adsorption data could be used to predict the adsorption of Th(IV) by the heterogeneous sand. In the absence of either geomedia, after forty-eight hours the measured pH-dependent “adsorption” was consistent with the solubility of solid amorphous ThO2(am, aged), despite the fact that ThO2(am, aged) is generally not formed until approximately seventy days. We concluded that ThO2(am, aged) was stabilized by precipitating on the walls of the reaction vessels. Ignoring this phenomenon could lead to experimental artifacts in Th(IV) adsorption studies. Thorium adsorption by both goethite and the sand was strongly pH dependent, with adsorption increasing sharply from pH ∼ 2 to pH ∼ 4. Two methods were utilized to predict the pH-dependent adsorption of Th(IV) by the sand using the Th(IV)-goethite adsorption data. Using the Fe content of the sand and the Th(IV)-goethite adsorption data, we were able to predict the maximum amount of Th(IV) adsorption by the sand within 78% of the actual value (i.e., an error of 22%). In contrast, on a surface-area-normalized basis, we were only able to predict the maximum adsorption of Th(IV) by the sand within a factor of two. These results have important implications to scaling and extrapolating the results of batch-scale tetravalent actinide adsorption studies with pure minerals to predict their field-scale adsorption by and transport in heterogeneous subsurface media.

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Section: Discussioncontrasting

confidence: 53%

Section: Thorium Adsorption To Geomediamentioning

confidence: 95%

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Adsorption of tetravalent thorium by geomedia

Melson¹,

Haliena²,

Kaplan³

et al. 2012

Radiochimica Acta

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“…In other words, only the fraction of surface area directly involved in the sorption process need be considered. The opposite has also been found experimentally; scaling uranium sorption behavior to total surface area gave better results than scaling to reactive surface area . Thus scaling to total surface area is more important.…”

Section: Extension Of Bench Data To Field Conditionsmentioning

confidence: 86%

Upscaling Sorption/Desorption Processes in Reactive Transport Models To Describe Metal/Radionuclide Transport: A Critical Review

Miller

Rodriguez

Honeyman

2010

Environ. Sci. Technol.

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Models are a mainstay of the environmental sciences; they allow for both deeper understanding of process knowledge and, to a limited extent, predictive capabilities of current day inputs on the future. Mathematical codes have become increasingly complex with explicit inclusion of many processes that could not be accounted for using simpler solving techniques. And yet, for metal/radionuclide transport in subsurface systems, the inclusion of smaller scale processes in a numerical solver do not always lead to better descriptions of larger scale behavior. The reasons for this are many, but included in this review are the following: unknowable conceptual model errors, discrepancy in the scale of model discretization relative to the scale of the chemical/physical process, and omnipresent chemical and physical heterogeneities. Although it is commonly thought that larger, more complex systems require more complex models to gain insight and predictive capability, there is little to no experimental evidence supporting this thought. Indeed, the evidence points to the fact that larger systems can be well described with simple models. To test this thought and to appreciate the incorporation of scaling behaviors into reactive transport modeling, new experiments are needed that are intermediate in scale between the more traditional bench and field scales.

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“…In this approach the mineral composition of interest is determined and known relevant surface complexation parameters for the mineral components are used in a predictive way in simulations. Comparisons of the approaches to various systems exist. ,,− The option of using the expected dominant sorbent in a complex sorbent has been successfully applied. ,− This short overview shows that there are various, often equally successful, applications of surface complexation models to handle complex situations.…”

Section: Geochemical Modeling Of Actinide Sorptionmentioning

confidence: 99%