Water desorption kinetics

Water desorption kinetics is referable to the Polanyi-Wigner equation, which is valid for an ideal (plane) energetically homogeneous surface, in which diffusion and readsorption phenomena are absent ... 

Quigley MS, Honeyman BD, Santschi PH (1996) Thorium sorption in the marine enviromnent equilibrium partitioning at the Hematite/water interface, sorption/desorption kinetics and particle tracing. Aquat Geochem 1 277-301... 

Chemical relaxation methods can be used to determine mechanisms of reactions of ions at the mineral/water interface. In this paper, a review of chemical relaxation studies of adsorption/desorption kinetics of inorganic ions at the metal oxide/aqueous interface is presented. Plausible mechanisms based on the triple layer surface complexation model are discussed. Relaxation kinetic studies of the intercalation/ deintercalation of organic and inorganic ions in layered, cage-structured, and channel-structured minerals are also reviewed. In the intercalation studies, plausible mechanisms based on ion-exchange and adsorption/desorption reactions are presented steric and chemical properties of the solute and interlayered compounds are shown to influence the reaction rates. We also discuss the elementary reaction steps which are important in the stereoselective and reactive properties of interlayered compounds. 

Earlier, Gavach et al. studied the superselectivity of Nafion 125 sulfonate membranes in contact with aqueous NaCl solutions using the methods of zero-current membrane potential, electrolyte desorption kinetics into pure water, co-ion and counterion selfdiffusion fluxes, co-ion fluxes under a constant current, and membrane electrical conductance. Superselectivity refers to a condition where anion transport is very small relative to cation transport. The exclusion of the anions in these systems is much greater than that as predicted by simple Donnan equilibrium theory that involves the equality of chemical potentials of cations and anions across the membrane—electrolyte interface as well as the principle of electroneutrality. The results showed the importance of membrane swelling there is a loss of superselectivity, in that there is a decrease in the counterion/co-ion mobility, with greater swelling. 

Diazinon and Ronnel. The conclusion that neutral hydrolysis of sorbed chlorpyrifos is characterized by a first-order rate constant similar to the aqueous phase value is strengthened and made more general by the results for diazinon, 0,0-diethyl 0-(2-iso-propyl-4-methyl-6-pyrimidyl) phosphorothioate, and Ronnel, 0,0-dimethyl 0-(2,4,5-trichlorophenyl) phosphorothioate (10). The results for the pH independent hydrolysis at 35°C for these compounds in an EPA-26 sediment/water system (p=0.040) are summarized in Table IV. Because the aqueous (distilled) values of k for diazinon and Ronnel are similar in magnitude to the value for chlorpyrifos, and because these values were shown by the chlorpyrifos study to be slow compared to sorption/desorption kinetics, computer calculations of were not deemed necessary and were not made for these data. 

Two of the recognized limitations of in situ technologies are (1) physicochemical restraints (e.g., bioavailability, desorption kinetics), and (2) a need for extended treatment time as compared to ex situ biotreatment approaches. Inherent geological parameters such as permeability, vertical and horizontal conductivity, and water depth can also represent constraints that are critically important to recognize and appreciate (Norris et al., 1993 Norris Falotico, 1994). Another widely recognized limitation inherent to in situ processes is that the systems are difficult to monitor and thus effective and complete treatment is difficult toascertain and validate. 

Kommalapati RR,Valsaraj KT, Constant WD (2000) Soil-water partition coefficients, adsorption/desorption hysteresis, desorption kinetics and bioavailability of chlorinated organic compounds at the PPI site. Submitted to Hazardous Substance Research Center, Louisiana State University, Baton Rouge, LA... 

Newns, A. C. The sorption and desorption kinetics of water in a regenerated cellulose. Trans. Faraday Soc. 52, 1533 (1956). 

Malhotra VM, Jasty S, Mu R (1989) FT-IR spectra of water in microporous KBr pellets and water s desorption kinetics Appl Spectrosc 43 638-645 Michell AJ (1988a) Note on a technique for obtaining infrared spectra of treated wood surfaces Wood Fiber Sci 20 272 -276... 

Tt is generally recognized that water plays an important role in main-taining skin in a healthy state with desirable mechanical properties (I). This work describes a technique for generating information on the state of water in the stratum corneum in vitro, with particular emphasis on the mobility of water in the corneum matrix and the eflEect of stratum corneum components on the characteristics of water diffusion. The characteristics of water diffusion in the stratum corneum are derived from sorption and desorption kinetics by using a gravimetric technique which allows determination of the amount of water vapor sorbed or desorbed continuously from an air stream of any given relative humidity. 

NMR has provided the most useful information on the state and mobility of water in keratins (2, 3, 4). It was shown (4) that the water associated with the stratum corneum seems to exist in two distinct states a bound fraction and a free fraction. This type of information could be obtained conveniently by the new technique using desorption kinetics under a wide range of experimental conditions. Also, it would be of interest to examine the effect of various agents, which are known to produce structural changes in the corneum, on the ability of the corneum to hold water and to retain it under a variety of conditions. 

An understanding of thermal desorption begins with an explanation of desorption kinetics. In thermal desorption systems, the portion of the contaminant in the liquid phase is removed as the soil temperature is increased above the boiling point of water and the contaminant. However, any portion of the contaminant bound to the soil must still be desorbed prior to removal. 

Desorption kinetics has been also studied the adsorbate is released because of unfavorable electrostatic conditions, change in temperature, or addition of reagents forming very stable water soluble complexes with the adsorbate of interest. 

Direct studies of the effect of pressure on surface charging are rare. The conductance of an anatase dispersion in HCI increased with pressure [179], This suggests a release of pre-adsorbed HCI from the surface at elevated pressure. On the other hand, the pressure effect was negligible in anatase dispersions in water or in NaCl. The experimental setup was designed to study desorption kinetics, and only the sign of the pressure effect could be determined. A similar method was used to study the pressure effect on proton adsorption on alumina dispersions in water [2928,3059], and in NaCl [2928], HNO,. and NaNO, [927] solutions, and the effect was negligible for a pressure of about 10 Pa. On the other hand, the same pressure had a substantial effect on uptake of heavy-metal cations [927] and of anions [2928,3059] on alumina. 

Stockman, H.W. 1997. A lattice gas study of retardation and dispersion in fractures Assessment of errors from desorption kinetics and buoyancy. Water Resour. Res. 33 1823-1831. 

Addition of soluble inorganic phosphorus to soil increases the soil pore water phosphorus concentration. This results in rapid adsorption of phosphorus onto soil surfaces to maintain equilibrium. Soil s capacity to adsorb additional phosphorus dictates the concentration of phosphorus in soil pore water. These adsorption processes occur within a short time period. When soil particles become saturated with phosphorus, there is an increase in phosphorus concentration in soil pore water. Reaction kinetics are on the order of minutes to hours to reach sorption equilibrium. Figure 9.21 illustrates a two-step process in which rapid phosphate exchange takes place between soil pore water and soil particles or mineral surface (adsorption) followed by slow penetration (absorption) of phosphate into solid phase. Similarly, desorption of phosphorus can also... 

Because many organic chemicals are nonionic and have low water solubilities, they will exist primarily in the sorbed state in soil- and sediment-water systems. The sorption of nonionic chemical occurs through hydrophobic sorption or partitioning to the organic matter associated with the soil or sediment (Karickhoff, 1980 Chiou et al., 1983). Furthermore, because desorption kinetics may be slow relative to hydrolysis kinetics, to accurately predict the fate of hydrolyzable chemicals in soil-and sediment-water systems an understanding of hydrolysis kinetics in the sorbed... 

Dissolved arsenic concentrations can be limited either by the solubility of minerals containing arsenic as a constituent element (or in solid solution) or by sorption of arsenic onto various mineral phases. For both the precipitation-dissolution of arsenic-containing minerals and sorption-desorption of arsenic onto solid phases, equilibrium calculations can indicate the level of control over dissolved arsenic concentrations that can be exerted by these processes. However, neither of these types of reactions is necessarily at equilibrium in natural waters. The kinetics of these reactions can be very sensitive to a variety of environmental parameters and to the level of microbial activity. In particular, a pronounced effect of the prevailing redox conditions is expected because potentially important sorbents (e.g., Fe(III) oxyhydroxides) are unstable under reducing conditions and because of the differing solubilities of As(V) and As(III) solids. 

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