Adsorption screening model

BIOSCREEN (Newell et al., 1996) is an easy-to-use screening model that simulates remediation through natural attenuation (RNA) of dissolved hydrocarbons at petroleum fuel release sites. The software, programmed in a spreadsheet environment and based on the Domenico analytical solute transport model, has the ability to simulate advection, dispersion, adsorption, and aerobic decay as well as anaerobic reactions that have been shown to be the dominant biodegradation processes at many petroleum release sites. 

Equation (89) shows that the allowance for the variation of the charge of the adsorbed atom in the activation-deactivation process in the Anderson model leads to the appearance of a new parameter 2EJ U in the theory. If U — 2Er, the dependence of amn on AFnm becomes very weak as compared to that for the basic model [see Eq. (79)]. In the first papers on chemisorption theory, a U value of 13eV was usually accepted for the process of hydrogen adsorption on tungsten. However, a more refined theory gave values of 6 eV.57 For the adsorption of hydrogen from solution we may expect even smaller values for this quantity due to screening by the dielectric medium. 

Rippen, G., Ilgenstein, M., Klopffer, W., Poreniski, H.J. (1982) Screening of the adsorption behavior of new chemicals natural soils and model adsorbents. Ecotox. Environ. Saf. 6, 236-245. 

Membrane-Screening Test Membrane-screening tests were performed to evaluate (1) the adequacy of flushing procedures, (2) the rejection of model compounds by the RO membrane, and (3) losses of model compounds to system components via adsorption, volatilization, solubility artifacts, or other phenomena. 

Reaction 14 shows an ion pair is formed with the oxide surface acting as a supramolecular counterion to which the TMI is bonded by ligand-screened electrostatic adsorption (Fig. 5, model III). 

Qualitatively, the zeroth-order Stern layer (flg. 3.20a) differs from the purely diffuse model in that the screening is poorer. Higher potentials are needed to obtain a certain surface charge. When there is specific adsorption (figs. 3.20b and c) a new feature emerges the non-electrostatlc contribution to the (Gibbs) energy of adsorption of counterions leads to an additional contribution to AG . It is recalled from sec. 3.2 that double layers form only because of non-electrostatlc affinities of ions for a surface. 

Simulation data on mixture adsorption can be used to screen zeolites as adsorbents, but experimental data are necessary to validate the simulations and to accurately design the separation process. The first step of the process design is to obtain such data. However, the experimental assessment of multi-component adsorption equilibria and kinetics is not straightforward and is highly time-consuming. As a result, some theories have been developed that predict adsorption behaviour for a mixture based on the pure component equilibria [1,3]. The isotherm data have to be correlated before their use in a design model... 

The major environmental fate processes for butyraldehyde in water are biodegradation and volatilization. A number of biological screening studies have demonstrated that butyraldehyde is readily biodegradable. Volatilization half-lives of 9h and 4.1 days have been estimated for a model river (Im deep) and an environmental pond, respectively. Aquatic hydrolysis, adsorption to sediment, and bioconcentration are not expected to be important fate processes. 

Aquatic fate If released to water, 2-heptanone is expected to rapidly volatalize to the atmosphere. The half-life for volatilization from a model river Im deep, flowing at Ims with a wind speed of 3ms is 8.4 h. The calculated bioconcentration factors ranging from 5.5 to 19 indicate that 2-heptanone is not expected to bioconcentrate in fish and aquatic organisms. The calculated soil adsorption coefficients ranging from 44 to 285 indicate that adsorption to sediment and suspended organic matter is not an environmentally important process. Screening... 

These assumptions are justifiable as the heat of adsorption of the small inert sorbate (e.g., N2 or Ar) is rather low and, hence, differences between sorption sites at the surface will be very small. Similarly, the interaction between the first and the following layers will be close to the heat of condensation, as the effect of polarization by the surface will be small beyond the first layer (screening of the long-range van der Waals forces). From its conception, the BET theory extends the Langmuir model to multilayer adsorption. It postulates that under dynamic equilibrium conditions the rate of adsorption in each layer is equal to the rate of desorption from that layer. Molecules in the first layer are located on sites of constant interaction strength and the molecules in that layer serve as sorption sites for the second layer and so forth. The surface is, therefore, composed of stacks of sorbed molecules. Lateral interactions are assumed to be absent. With these simplifications one arrives at the BET equation... 

Fig. 4.10. Sketch of adsorption of polydisperse particles at (a) low and (b) high salt concentrations. Dotted lines show the effective particle radius (or interaction distance), (c) Surface coverage of the polystyrene particles versus na ( a is a dimensionless screening parameter, where k is the inverse Debye length and a the particle diameter). The more polydisperse particles (41 versus 107nm) have a slightly increased coverage at high na. Solid curves are approximations derived from the effective hard sphere model (see [89] for further details)...

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