Sorption experimental details

Figure I. Arsenate sorption kinetics, batch experiments (experimental details see text)...

Because several recent papers have reviewed the applications of XAFS spectroscopy to sorption complexes at mineral/solution interfaces (e g., Brown et al. 1999c Brown and Parks 2001), here we list many of the sorption systems that have been studied over the past 15 years using XAFS spectroscopy methods (Appendix — Tables 1 and 2) without detailed discussion of results. The interested reader is directed to the individual papers listed in Tables 1 and 2 (see Appendix) for experimental details and results and to Brown and Parks (2001) for a detailed discussion of many sorption systems of relevance to low temperature geochemistry and environmental science. 

Upton RN, Runciman WB and Mather LE, Relationship between some physico-chemical properties of ionizable drugs and their sorption into medical plastics, Aust. /. Hosp. Pharm., 17, 267-270 (1987). NB no references or experimental details were given to support the stated value. 

Plutonium uptake on geologic media under various conditions have been studied extensively during the last few years, and reviewed (e.g. in ref. 60). It should be emphasized that data from various experiments are rarely directly comparable, due to differences in experimental techniques, chemical conditions and other parameters of importance. A detailed discussion of sorption data is outside the scope of this paper. 

A typical sorption experiment involves exposing a polymer sample, initially at an equilibrium penetrant concentration of c to a bathing penetrant concentration of Ci. The weight gain or loss is then measured as a function of time. The term sorption used in this context includes both absorption and desorption. The sorption is of the integral type if c° = 0 in the case of absorption or if cf = 0 in the case of desorption. Details of the experimental setup for the sorption measurement are discussed elsewhere [4],... 

Loukidou et al. (2005) fitted the data for the equilibrium sorption of Cd from aqueous solutions by Aeromonas caviae to the Langmuir and Freundlich isotherms. They also conducted, a detailed analysis of sorption rates to validate several kinetic models. A suitable kinetic equation was derived, assuming that biosorption is chemically controlled. The so-called pseudo second-order rate expression could satisfactorily describe the experimental data. The adsorption data of Zn on soil bacterium Pseudomonas putida were fit with the van Bemmelen-Freundlich model (Toner et al. 2005). 

The main peculiarities of the preferential sorption phenomenon have been experimentally examined in detail in a series of papers by Semchikov, Smirnova et al. [61-76]. Investigating the free-radical copolymerization in bulk of about 30 concrete pairs of the most commonly encountered vinyl monomers, they revealed the following characteristic features of this phenomenon ... 

In this review, we focus on the information at an atomic/molecular level that is obtainable via the different techniques. The precise methods and techniques used are not extensively discussed instead we summarize the relevant details and direct the reader toward key references. Nor do we review the potentials that are used in the classical simulations of sorption and diffusion. Derivation and evaluation of these parameters require extensive comparison with detailed spectroscopic data and are beyond the scope of this work. Similarly, the volume of experimental results that may be used in comparison to the calculations is vast. We use representative data taken largely from reviews or books. 

The packed bed breakthrough method for investigation of mass transfer phenomena in sorbent systems can in many instances offer certain advantages not found in other experimental methods. The method is especially useful when the adsorption isotherms for the principal sorbate exhibit favorable curvature (convex toward loading axis). In such a case, there is the potential for a portion of the sorption front to approach a stable wave form (shape of the front invariant with time). Given the existence of a stable or "steady-state" mass transfer zone (MTZ) and a detailed knowledge of the equilibrium loading characteristics within that zone, one can extract local values of the effective mass transfer resistance at any concentration in the zone. 

Correlation of the permeation properties of a wide variety of polymers with their free volume is not possible [32], But, within a single class of materials, there is a correlation between the free volume of polymers and gas diffusion coefficients an example is shown in Figure 2.24 [33], The relationship between the free volume and the sorption and diffusion coefficients of gases in polymers, particularly glassy polymers, has been an area of a great deal of experimental and theoretical work. The subject has recently been reviewed in detail by Petropoulos [34] and by Paul and co-workers [35,36],... 

This chapter details the findings of the sorption/desorption hysteresis and desorption kinetic studies and how the results of these environmental chemodynamic studies impacted remediation of the PPI sites. The literature on the topic is presented below.. In the next section, we present some of the results of our research on sorption/desorption hysteresis and desorption kinetics for freshly contaminated soils as well as aged soils. The experimental protocols are published elsewhere [6-10]. 

The most widely used unsteady state method for determining diffusivities in porous solids involves measuring the rate of adsorption or desorption when the sample is subjected to a well defined change in the concentration or pressure of sorbate. The experimental methods differ mainly in the choice of the initial and boundary conditions and the means by which progress towards the new position of equilibrium is followed. The diffusivities are found by matching the experimental transient sorption curve to the solution of Fick s second law. Detailed presentations of the relevant formulae may be found in the literature [1, 2, 12, 15-17]. For spherical particles of radius R, for example, the fractional uptake after a pressure step obeys the relation... 

Diffusion of hydrocarbons and other simple molecules in A, X and Y zeolites has been studied by a range of experimental methods including direct sorption rate measurements, chromatography and NMR. The advantages and limitations of these techniques are considered and results of recent experimental studies are reviewed with emphasis on the detailed microdynamic information obtainable by NMR. 

Earlier studies of intracrystalline diffusion in zeolites were carried out almost exclusively by direct measurement of sorption rates but the limitations imposed by the intrusion of heat transfer and extra-crystalline mass transfer resistances were not always fully recognized. As a result the reported diffu-sivities showed many obvious inconsistencies such as differences in diffusivity between adsorption and desorption measurements(l-3), diffusivities which vary with fractional uptake (4) and large discrepancies between the values measured in different laboratories for apparently similar systems. More recently other experimental techniques have been applied, including chromatography and NMR methods. The latter have proved especially useful and have allowed the microdynamic behaviour of a number of important systems to be elucidated in considerable detail. In this paper the advantages and limitations of some of the common experimental techniques are considered and the results of studies of diffusion in A, X and Y zeolites, which have been the subject of several detailed investigations, are briefly reviewed. 

By combining thermodynamically-based monomer partitioning relationships for saturation [170] and partial swelling [172] with mass balance equations, Noel et al. [174] proposed a model for saturation and a model for partial swelling that could predict the mole fraction of a specific monomer i in the polymer particles. They showed that the batch emulsion copolymerization behavior predicted by the models presented in this article agreed adequately with experimental results for MA-VAc and MA-Inden (Ind) systems. Karlsson et al. [176] studied the monomer swelling kinetics at 80 °C in Interval III of the seeded emulsion polymerization of isoprene with carboxylated PSt latex particles as the seeds. The authors measured the variation of the isoprene sorption rate into the seed polymer particles with the volume fraction of polymer in the latex particles, and discussed the sorption process of isoprene into the seed polymer particles in Interval III in detail from a thermodynamic point of view. 

The experimental approach for obtaining sorption and desorption isotherms as well as hysteresis eflFects is well known and will not be discussed further. However, diflFusion measurements will be given a somewhat more detailed treatment. 

Small amounts of water within a zeolite can have a large effect on some experiments, so complete dehydration is often necessary. A zeolite which is to be exposed to alkali-metal vapor, for example, must not be given an opportunity to resorb water fi-om other parts of its vessel after dehydration but before metal vapor sorption. The resulting metal hydroxide or oxide (additional products) could lead to the destruction of the zeolite. To compound the problem, the experimental conditions are often not described in detail in a report in the literature, so the reader can only be suspicious of a link between the reported result and inadequate dehydration. For some work, involving large amounts of powder, this problem may sometimes be of minor importance. Where tiny samples are involved, it is crucial. 

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