Modeling the effectiveness of U(VI) biomineralization in dual-porosity porous media

Rotter, B. E.; Barry, David Andrew; Gerhard, Jason I.; Small, Joe S.

doi:10.1016/j.jhydrol.2011.02.029

Cited by 5 publications

(3 citation statements)

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“…Both mobile and immobile domains have uranium sorption sites. The dual-domain representation in PHREEQC has been used previously for reactive transport. , The code solves the mass conservation eqs and ) integrating flow, transport, and geochemical reactions. , A representative equation for species i is as follows where the subscripts m and im represent mobile and immobile domains; θ is porosity; C i and M i are the aqueous and adsorbed concentration (mol/m 3 ), respectively, with the latter calculated by normalizing sorbed mass by the mobile and immobile pore volumes; D L is the hydrodynamic dispersion (m 2 /s); u is the flow velocity (m/s); R i is the total rate of kinetically controlled reactions that species i is involved in (mol/m 3 /s); N is the total number of aqueous species. The first-order mass transfer coefficient (α, s –1 ) relates to specific geometries of the immobile zones reflecting spatial heterogeneity with the following relation where D e is the effective diffusion coefficient in porous media (m 2 /s), r is the radius of the assumed sphere shape for the immobile zones (m), and f s→1 is a shape factor for sphere-to-first-order-model conversion.…”

Section: Methodsmentioning

confidence: 99%

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Enhanced Uranium Immobilization by Phosphate Amendment under Variable Geochemical and Flow Conditions: Insights from Reactive Transport Modeling

Wen

Pan

Giammar

et al. 2018

Environ. Sci. Technol.

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Phosphate amendment has shown promise for enhancing uranium immobilization. The mechanism of the enhancement, however, has remained unclear with contrasting observations under variable environmental conditions. A dual-domain reactive transport model is developed here with constraints from batch and column experimental data to understand the mechanisms and to explore the effectiveness of enhanced U(VI) immobilization under variable geochemical and flow conditions. Modeling results indicate that under low U(VI) conditions in natural waters, phosphate addition promotes U(VI) immobilization through the formation of U(VI)-phosphate ternary surface complexes and the precipitation of calcium phosphate, both decreasing the concentrations of mobile U-Ca-CO aqueous complexes. This contrasts with previous hypotheses attributing the immobilization enhancement to U(VI)-phosphate precipitation under experimental conditions with high U(VI). Sensitivity analysis shows that phosphate is effective under relatively low Ca (<0.1 mM) and total inorganic carbon (TIC) (<0.5 mM) conditions, where >60% of U(VI) still remains on sediments after 113 residence times of flushing with low phosphate solutions (<0.1 mM). Under high Ca or TIC conditions, a similar level of U(VI) immobilization can be achieved only when the phosphate concentration is higher than Ca or TIC concentrations. Compared to the strong geochemical effects, flow conditions have relatively limited impacts on U(VI) immobilization. These results explain contrasting field observations on the effectiveness of phosphate amendment and offer capabilities to extrapolate observations to other environmental conditions.

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Section: Methodsmentioning

confidence: 99%

“…The dual-domain representation in PHREEQC has been used previously for reactive transport. 35,36 The code solves the mass conservation eqs 1 and 2) integrating flow, transport, and geochemical reactions. 34,37 A representative equation for species i is as follows Figure 1.…”

Section: ■ Methodsmentioning

confidence: 99%

Enhanced Uranium Immobilization by Phosphate Amendment under Variable Geochemical and Flow Conditions: Insights from Reactive Transport Modeling

Wen

Pan

Giammar

et al. 2018

Environ. Sci. Technol.

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“…Note that the model does not include diffusive processes in the flowing water. This could be included (e.g., Ma and Selim (1996); Bajracharya and Barry (1997); Rotter et al (2011)), but at the cost of an additional parameter. Note that the model does yield diffusive-like behaviour.…”

Section: Methodsmentioning

confidence: 99%

Modelling city-scale facade leaching of biocide by rainfall

et al. 2012

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t r a c tA methodology is presented for estimating, at the city scale, the amount of biocide released from facades during rain events. The methodology consists of two elements. First, leaching of a single facade is simulated using a two-region model, one region for the biocide in the facade and the other for that in the flow over the facade surface. In the latter region, water advection moves the biocide to the base of the facade, and so into the environment. Rates of detachment and deposition define the exchange process between the two regions. The two-region model was calibrated on laboratory data, and afterward applied at city scale to Lausanne, Switzerland (200,000 inhabitants). The city-scale application uses the second element of the methodology, which consists of an estimate of the exposure of the city's facades to rainfall, and relating that rainfall to the over-facade flow in the calibrated singlefacade model. This results in a straightforward translation of over-facade flow volume to facade paint age, a necessary connection since facade leaching is dependent on paint age.For Lausanne, it was estimated that approximately 30% of the mass of biocides applied annually is released into the environment.ª 2012 Elsevier Ltd. All rights reserved. IntroductionBiocides are substances designed to destroy, repulse or make harmless adverse organisms via a chemical or biological reaction, as described, for example, in the European Parliament Directive 98/8/CE (E. U., 1998). Their presence in the natural environment can affect fauna and flora even at low concentrations (Chè vre et al., 2006;Mohr et al., 2009;Wittmer et al., 2011a). Agriculture has traditionally been the main source of environmental contamination by pesticides. However, recent studies have demonstrated that the same compounds in urban environment, which have multiple and complex origins (Wittmer and Burkhardt, 2009), should be considered also (Schoknecht et al., 2003;Wittmer et al., 2010). These substances, when present in the urban environment, are usually named biocides. Biocides contained in exterior building paints are often considered as a major contamination source (Burkhardt et al., 2011). Indeed, fungicides and algaecide are frequently used in resin-based paints and renders to prevent the growth of organisms that would otherwise colonize facades under moist conditions (Shirakawa et al., 2002). These products are widespread, accounting for more than 95% of the insulated facade market (Burkhardt et al., 2011).Surfaces treated with biocides and exposed to rainfall can potentially be leached and thereby release biocides into the environment. The main physico-chemical factors controlling facade leaching are dissolution, complexation, sorption, diffusion, percolation and surface wash-off (Hall, 1977; Van der Sloot et al., 2008). For a given substance, leaching rates are influenced by pH, type of reactive surface in contact with it, and water phase composition (Appelo and Postma, 2005).Detailed mechanistic models of these processes for building facad...

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Simulating biodegradation under mixing-limited conditions using Michaelis–Menten (Monod) kinetic expressions in a particle tracking model

Ding

Benson

2015

Advances in Water Resources

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Modeling the effectiveness of U(VI) biomineralization in dual-porosity porous media

Cited by 5 publications

References 88 publications

Enhanced Uranium Immobilization by Phosphate Amendment under Variable Geochemical and Flow Conditions: Insights from Reactive Transport Modeling

Enhanced Uranium Immobilization by Phosphate Amendment under Variable Geochemical and Flow Conditions: Insights from Reactive Transport Modeling

Modelling city-scale facade leaching of biocide by rainfall

Simulating biodegradation under mixing-limited conditions using Michaelis–Menten (Monod) kinetic expressions in a particle tracking model

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