Mobile immobilization

Therefore, Eq. 10.5 is limited in its applicability, as are variations of this equation such as the mobile-immobile one (see Sect. 10.2). We discuss non-Fickian transport in detail in Sect. 10.3. 

To quantify such transport, the advection-dispersion equation, which requires a narrow pore-size distribution, often is used in a modified framework. Van Genuchten and Wierenga (1976) discuss a conceptualization of preferential solute transport throngh mobile and immobile regions. In this framework, contaminants advance mostly through macropores containing mobile water and diffuse into and out of relatively immobile water resident in micropores. The mobile-immobile model involves two coupled equations (in one-dimensional form) ... 

The previous sections discussed the advection-dispersion equation and variants such as the mobile-immobile conceptualization, which are based on the key assumption that mechanical dispersion is Fickian. In other words, the advection-dispersion equation (Eq. 10.5) is strictly valid only under perfectly homogeneous... 

Another modeling analysis is presented by Russo et al. (1998), who examined field transport of bromacil by application of the classical one-region, advection-dispersion equation (ADE) model and the two region, mobile-immobile model (MM) recall Sects. 10.1 and 10.2. The analysis involved detailed, three-dimensional numerical simulations of flow and transport, using in-situ measurements of hydraulic... 

Fig. 12.7 Profiles of means (a,b) and standard deviations (c,d) of the bromacil concentrations at four different time points. Solid curves denote simulated profiles obtained from the advection-dispersion equation (a,c) and the mobile-immobile model (b,d). The different symbols denote measured profiles at different times. Reprinted from Russo D, Toiber-Yasur I, Laufer A, Yaron B (1998) Numerical analysis of field scale transport of bromacil. Adv Water Resour 21 637-647. Copyright 1998 with permission of Elsevier...

The Fe " formed this way is mobile in the soil mantle and moves in (by diffusion) or together with (by convection) the soil water until it reaches aerobic environments where it is reoxidized and reprecipitated, often as Fe "oxides. Such processes lead to characteristic colour patterns in the soil mantle (redoximorphosis) which reflect the mobilizing/immobilizing processes (Schwertmann Fitzpatrick, 1992 Schwert-mann, 1993). The distances over which Fe " migrates range from between 10 -1 m within soil profiles to up to lO" " m in landscapes. 

Mechanistic Multiphase Model for Reactions and Transport of Phosphorus Applied to Soils. Mansell et al. (1977a) presented a mechanistic model for describing transformations and transport of applied phosphorus during water flow through soils. Phosphorus transformations were governed by reaction kinetics, whereas the convective-dispersive theory for mass transport was used to describe P transport in soil. Six of the kinetic reactions—adsorption, desorption, mobilization, immobilization, precipitation, and dissolution—were considered to control phosphorus transformations between solution, adsorbed, immobilized (chemisorbed), and precipitated phases. This mechanistic multistep model is shown in Fig. 9.2. 

Gamerdinger, A. P., andKaplan, D. I. (2000). Application ofa continuous-flow centrifugation method for solute transport in disturbed, unsaturated sediments and illustration of mobile-immobile water. Water Resour. Res. 36(7), 1747-1755. 

Finally, the NMR and the dynamic mechanical study show that two regions are present in filled silicone rubbers above the Tg, which differ significantly in local chain mobility immobilized chain units adsorbed at the filler surface and mobile chain units outside the adsorption layer. The local chain motions outside the adsorption layer are similar to those for unfilled rubbers. Chain motions in the adsorption layer however are strongly restricted. The frequency of chain motions in the adsorption layer at 300 K is comparable to the fi-equency of chain motions in a crosslinked PDMS containing 3-4 elementary chain units between network junctions [26]. 

There are now two possible routes to explore (1) make the suspension less stable, but still avoiding agglomeration in the suspension, that is, sufficient to induce the mobile-immobile transition across the whole layer and (2) sustain the capillary pressure during drainage. 

Figures 4-5). Sorption was reversible, and was not affected by a lag of up to 60 days between sorption and desorption (e.g. Figure 4). Fitted parameters for 29 column experiments for which good convergence was obtained for the first-order and mobile-immobile models are presented in Table III. Equilibrium-model parameters are presented for an additional 11 experiments. The full data sets for these experiments can be found in Szecsody (8). 

To separate slow kinetics due to mobile-immobile transfer, binding-release or intraparticle diffusion fi-om dispersion in the mobile phase, it is necessary to have an independent estimate of D for the organic solutes (as defined by equation 1). Horvath and Lin (11) analyzed hydrodynamic dispersion of organic solutes versus ionic tracers in liquid chromatography using an empirical approach ... 

Although the mobile-immobile model provides another parameter (P or /), it does not have a clear interpretation in the experimental system studied. Particles used in this work have 99 percent of the surface internal and only 1 percent external, suggesting that / should be small. As / approaches 0, the mobile-immobile model becomes equivalent to the first-order model. Larger values of / could be interpreted as indicating that there is fast exchange of solute with internal pores. In fitting breakthrough curves, consistent values off between experiments were not often obtained. 

Jaynes, D.B., Logsdon, S.D., and Horton, R. (1995) Field method for measuring the mobile/immobile water and solute transfer rate coefficient. Soil Science Society of America Journal 59 352-356. 

Help in the mobilization/immobilization of phosphate and trace metals Alter pH/alkalinity... 

Having discussed the notion of the electrokinetic potential, we will now focus on the different electrokinetic phenomena, which can be distinguished by the mobile-immobile phases, the nature of the applied field, and the quantity that must be experimentally determined. A brief list of definitions follows ... 

Key words bioaccumulation — biomonitoring — environmental specimen bank — mobilization/immobilization of pollutants — retrospective analysis... 

Modelling, Simulation and Control of the Dyeing Process MIM (Mobile-Immobile Model)... 

In imsaturated medium, especially at low water content, the liquid phase is not fully connected, and therefore not fully participating to the flow. In such a situation. Equation 15.6 must be augmented by a sink term that accounts for mass exchange by diffusion toward stagnant zones. This type of model is usually referred to as a mobile-immobile model, or a two-region model (Coats and Smith, 1964 van Genuchten and... 

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