Kinetics, sorption

Sorption kinetics Sorption and desorption may not always be fast compared to other processes, such as advection and dispersion. In addition, the sorption equilibrium does not necessarily follow a linear relationship. 

When extrapolated to a 1-meter barrier typical of field installations, predictions that incorporated kinetic sorption were essentially identical to those generated using an equilibrium model, due to the low hydraulic gradient and larger domain associated with field conditions. 

Selim et al. (1976b) developed a simplified two-site model to simulate sorption-desorption of reactive solutes applied to soil undergoing steady water flow. The sorption sites were assumed to support either instantaneous (equilibrium sites) or slow (kinetic sites) first-order reactions. As pore-water velocity increased, the residence time of the solute decreased and less time was allowed for kinetic sorption sites to interact (Selim et al., 1976b). The sorption-desorption process was dominated by the equilib-... 

The comparison of kinetic sorption models presented here was made possible by the use of the mixing-cell dynamic technique, which eliminates the masking effects of hydraulic dispersion. 

One of new methods of magnesium, transition and rare-earth metals hydrides and their compounds obtaining is mechanical-chemical method. Numerous quantity of works are devoted to the improving kinetic, sorption properties of hydrides which were treated mechanically or were obtained by this method in hydrogen medium under pressure [1-7]. Great consideration is given to the influence of dispersity on phase equilibrium. At the same time the investigation of mechanical... 

The kinetic sorption data can be interpreted based on the assumption that the uranium sorbs on the surface of granite according to a first-order reaction. The time dependence can be given as ... 

Laboratory experiments, transport modeling, field data, and engineering cost analysis provide complementary information to be used in an assessment of the viability of an MNA approach for a site. Information from kinetic sorption/ desorption experiments, selective extraction experiments, reactive transport modeling, and historical case analyses of plumes at several UMTRA sites can be used to establish a framework for evaluation of MNA for uranium contamination (Brady et al, 1998, 2002 Bryan and Siegel, 1998 Jove-Colon et al, 2001). The results of a recent project conducted at the Hanford 100-N site provided information for evaluation of MNA for a °Sr plume that has reached the Columbia River (Kelley et al, 2002). The study included strontium sorption-desorption studies, strontium transport and hydrologic modeling of the near-river system, and evaluation of the comparative costs and predicted effectiveness of alternative remediation strategies. 

Nonlinear sorption of chem-bio agents can be based on the different kinetics of sorption. Chemical nonequilibrium must also be considered in real-world problems. One of the early kinetic sorption models used the CDE first-order reactions (Scott 2000). This is represented as follows ... 

Two model approaches are compared by simulating reactive transport of acenaphthene in a heterogeneous porous medium. In a Monte Carlo approach a Lagrangian onedimensional streamtube model is used to assess the transport behaviour at field scale for distances of up to 800 m. Aquifer properties are taken from results of field experiments characterising a test site in a shallow quaternary sand and gravel aquifer. The results of the streamtube model are compared to model results of a two-dimensional Eulerian model. Both models account for kinetic sorption, described as diffusive transport in intra-particle pores. 

Linearization of kinetic data. Jannasch and co-workers (17) have developed a very useful approach to identify the number of distinct processes that contribute to the observed overall kinetics and, hence, need to be considered in the development of a suitable kinetic model to evaluate the data. These authors have derived a linearized equation for kinetic sorption controlled by a number of separate processes. Their analysis assumes that only one process controls overall sorption at any time and that each process can be described by a first order reversible reaction ... 

Sorption characteristics, which comprise sorption kinetics, sorption isotherms, and sorption capacity, determine the efficiency of contact-sorption drying and selection of the drying method and dryer design. 

Adsorption may also be modeled as a nonequilibrium process using nonequilibrium kinetic equations. In a kinetic model, the solute transport equation is linked to an appropriate equation to describe the rate that the solute is sorbed onto the solid surface and desorbed from the surface (Fetter, 1999). Depending on the nonequilibrium condition, the rate of sorption may he modeled using an irreversible first-order kinetic sorption model, a reversible linear kinetic sorption model, a reversible nonlinear kinetic sorption model, or a bilinear adsorption model (Fetter, 1999). 

Batch-experiments are well suited for the measurement of sorption kinetics on defined soil components such as oxides or clay minerals. For the transformation of kinetic data from these batch-experiments to transport processes in model soil columns attention has to be paid to the dependence of the kinetic sorption parameters on the concentration of the suspended particles. 

In the studies presented the model developed for sorption equilibrium [1] was extended also to sorption kinetics. Furthermore, an approximative procedure was outlined for the transformation of equilibrixim and kinetic sorption data from batch-experiments to transport processes in model soil columns. 

An approximative method for the transformation of kinetic sorption data... 

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