Sorption processes definition

The ability of palladium to adsorb or absorb large amounts of hydrogen was known before the end of the last century. Much more precise work has been reported in recent years (I, 2, 3, 18). Such studies accurately showed the dependence of the sorption process on pressure and temperature. The isotherms generally indicated a sudden increase in the sorption of hydrogen at a certain pressure, which was very temperature-dependent. This sudden rise in the amounts sorbed at definite pressures suggested a phase shift in the crystalline structure of the palladium from a hydrogen-poor cr-phase to a hydrogen-rich / -phase. Such... 

The formation of 2D Meads phases on a foreign substrate, S, in the underpotential range can be well described considering the substrate-electrolyte interface as an ideally polarizable electrode as shown in Section 8.2. In this case, only sorption processes of electrolyte constituents, but no Faradaic redox reactions or Me-S alloy formation processes are allowed to occur, The electrochemical double layer at the interface can be thermodynamically considered as a separate interphase [3.54, 3.212, 3.213]. This interphase comprises regions of the substrate and of the electrolyte with gradients of intensive system parameters such as chemical potentials of ions and electrons, electric potentials, etc., and contains all adsorbates and all surface energy. Furthermore, it is assumed that the chemical potential //Meads is a definite function of the Meads surface concentration, F, and the electrode potential, E, at constant temperature and pressure Meads (7", ). Such a model system can only be... 

It should be recognized that adsorption isotherms are purely descriptions of macroscopic data and do not definitively prove a reaction mechanism. For example, the conformity of experimental adsorption data to a particular isotherm does not indicate that this is a unique description of the experimental data, and that only adsorption is operational. Thus, one cannot differentiate between adsorption and other sorption processes, such as surface precipitation, and diffusion using an adsorption isotherm, even though this has been done in the geochemistry literature. 

Dent and Kohes (27) proposed a definite bond between propylene and zinc oxide, infrared spectroscopy being used to study the sorption process. A series of articles by Gil-Av et al. (28-31) demonstrated the use of stationary phases containing silver nitrate to separate saturated and unsaturated compounds. 

Chromatography is essentially a physical method of separation in trtiich the components to be separated are distributed between two phases one of which is stationary (stationeury phase) while the other (the mobile phase) percolates through it in a definite direction. The chroaatographic process occurs as a result of repeated sorption/desorption acts during the movement of the sample components along the stationary bed, and the separation is due to differences in the distribution constants of the Individual sample components. 

The clay fraction, which has long been considered as a very important and chemically active component of most solid surfaces (i.e., soil, sediment, and suspended matter) has both textural and mineral definitions [22]. In its textural definition, clay generally is the mineral fraction of the solids which is smaller than about 0.002 mm in diameter. The small size of clay particles imparts a large surface area for a given mass of material. This large surface area of the clay textural fraction in the solids defines its importance in processes involving interfacial phenomena such as sorption/desorption or surface catalysis [ 17,23]. In its mineral definition, clay is composed of secondary minerals such as layered silicates with various oxides. Layer silicates are perhaps the most important component of the clay mineral fraction. Figure 2 shows structural examples of the common clay solid phase minerals. 

The main goal of this chapter is to review the most widely used modeling techniques to analyze sorption/desorption data generated for environmental systems. Since the definition of sorption/desorption (i.e., a mass-transfer mechanism) process requires the determination of the rate at which equilibrium is approached, some important aspects of chemical kinetics and modeling of sorption/desorption mechanisms for solid phase systems are discussed. In addition, the background theory and experimental techniques for the different sorption/ desorption processes are considered. Estimations of transport parameters for organic pollutants from laboratory studies are also presented and evaluated. 

The main reasons for investigating the rates of solid phase sorption/desorption processes are to (1) determine how rapidly reactions attain equilibrium, and (2) infer information on sorption/desorption reaction mechanisms. One of the important aspects of chemical kinetics is the establishment of a rate law. By definition, a rate law is a differential equation [108] as shown in Eq. (32) ... 

Bio)chemical sensors can be active or passive according to whether they use a sensing microzone to accommodate a chemical or biochemical reaction and/or a biochemical e.g. immunological) or physico-chemical separation e.g. sorption). It should be noted that passive sensors e.g. a fibre-optic tip immersed in an industrial process stream) do not meet one of the essential requirements included in the definition of sensors as regeirds composition... 

The first step in the estimation process is the definition of a normalized sorption coefficient, K, defined as... 

PROBABLE FATE photolysis photooxidation definitely occurs, photooxidation half-life in water 3.2-160 days photooxidation half-life in air 1.19-11.9 hrs oxidation metal-catalyzed oxidation occurs in aerated surface waters, oxidation by peroxy radicals is important, photochemically produced hydroxyl radicals degrades compound in daylight hours, half-life 8 hrs hydrolysis not an important process volatilization not an important process sorption slight potential for adsorption onto organic materials, adsorption to sediment will be moderate biological processes biodegradation can occur other reactions/interactions chlorine present in water could chlorinate the eompound can be washed out by rain... 

This definition of indicates a coefficient dependent only on the partition properties of a substance between two phases (organic carbon and water) and independent of other possible processes of sorption or other interactions with the inorganic matrix of the soil. 

This term denotes distribution of a compound into/onto a sod or sediment without considering a specific mechanism. Soils are so complex that in some situations several mechanisms could be active and in an experimental context, on occasion, one could simply be observing inclusion in some pore in the sod structure distinct from any of the processes discussed. Thus sorption is a more inclusive and less definitive term and would be a more appropriate designator for the distribution of chemicals between soil and water. 

It is important to note that this approach is guided by the idea not to characterise and map the spatial variability of a specific functional or structural property, for example the hydraulic conductivity or the coefficients for sorption (Rubin and Gomez-Her-nandez, 1990 Koltermann and Gorelick, 1996), but rather to characterise the spatial variability of the structures themselves (Carle et al., 1998), that are the pedofacies in this study. Once this is achieved, the spatial distribution of these entities is reconstructed and used as a template for the definition of the spatial distribution of process parameters. 

---