Sorption model, physicochemical

A substantial number and variety of models of gas transport in polymers have been proposed during the last 20-30 years, in view of the great practical and scientific importance of this process. Molecular-type models are potentially most useful, since they relate diffusion coefficients to fundamental physicochemical properties of the polymers and penetrant molecules, in conjunction with the pertinent molecular interactions. However, the molecular models proposed up to now are overly simplified and contain one or more adjustable parameters. Phenomenological models, such as the dual-mode sorption model and some free-volume models, are very useful for the correlation and comparison of experimental data. 

The pronounced effects of aqueous chemistry on actinide sorption behavior suggest that sorption modeling should account for changing physicochemical conditions. A number of different modeling approaches of varying complexity can be used to incorporate the effects of chemistry on radionuclide sorption. A class of models that has been used with success in modeling pH-dependent sorption for actinides and other metals is the electrostatic surface complexation model (SCM). These models are equilibrium representations of sorption at the mineral-water interface and are discussed in detail elsewhere (Davis Kent, 1990 Dzombak Morel, 1990 Hayes etal., 1991 Seme etal., 1990 Turner, 1995), with only a brief overview presented here. 

Pollutants with high VP tend to concentrate more in the vapor phase as compared to soil or water. Therefore, VP is a key physicochemical property essential for the assessment of chemical distribution in the environment. This property is also used in the design of various chemical engineering processes [49]. Additionally, VP can be used for the estimation of other important physicochemical properties. For example, one can calculate Henry s law constant, soil sorption coefficient, and partition coefficient from VP and aqueous solubility. We were therefore interested to model this important physicochemical property using quantitative structure-property relationships (QSPRs) based on calculated molecular descriptors [27]. 

Chemical reactivity and biological activity can be related to molecular structure and physicochemical properties. QSAR models can be established among hydrophobic-lipophilic, electronic, and steric properties, between quantum-mechanics-related parameters and toxicity and between environmental fate parameters such as sorption and tendency for bioaccumulation. The main objective of a QSAR study is to develop quantitative relationships between given properties of a set of chemicals and their molecular descriptors. To develop a valid QSAR model, the following steps are essential ... 

Substantial efforts have been made to develop physicochemical models for ion exchange based on the Gouy-Chapman diffuse-layer theory (e.g., 9, 10). This work not only has provided insight into the role of diffuse-layer sorption in the ion-exchange process but also has pointed to the need to consider other factors, especially specific sorption at the surface. Consideration of specific sorption enables description of the different tendencies of ions to... 

Several physicochemical models of ion exchange that link diffuse-layer theory and various models of surface adsorption exist (9, 10, 14, 15). The difficulty in calculating the diffuse-layer sorption in the presence of mixed electrolytes by using analytical methods, and the sometimes over simplified representation of surface sorption have hindered the development and application of these models. The advances in numerical solution techniques and representations of surface chemical reactions embodied in modem surface complexation mod-... 

Physicochemical models of partitioning at the solid-water interface, such as that used here to model ion exchange, require detailed knowledge about the particles. The surface properties of the mineral phases present, as well as equilibrium constants for ion binding to both fixed and variable charge sites associated with each phase, are required. These data requirements and the uncertainty about modeling sorption in mixtures of minerals (e.g., 48-50) make such models difficult to apply to complex natural systems. This is especially the case for modeling solute transport in soil-water systems, which... 

A series of related experiments investigated nonionic surfactant sorption onto soil, mechanisms of nonionic surfactant solubilization of polycyclic aromatic hydrocarbon (PAH) compounds from soil, and microbial mineralization of phenanthrene in soil-aqueous systems with nonionic surfactants. Surfactant solubilization of PAH from soil at equilibrium can be characterized with a physicochemical model by using parameters obtained from independent tests in aqueous and soil-aqueous systems. The microbial degradation of phenanthrene in soil-aqueous systems is inhibited by addition of alkyl ethoxylate, alkylphenyl ethoxylate, or sorbitan- (Tween-) type nonionic surfactants at doses that result in micellar solubilization of phenanthrene from soil. Available data suggest that the inhibitory effect on phenanthrene biodegradation is reversible and not a specific, toxic effect. 

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