Sorption of ions

The sorption of ions of heavy metals (Cu(II), Zn(II), Cr(VI), Cd(II), Pb(II)) on ChCS in static and dynamic conditions were studied. For an estimation of selective sorbate ability ChCS the distribution factor was determined. Sorption, physical and chemical properties of complexes received by different methods were analyzed by a compai ative method. 

Liu, H. and Cantwell, F.F. Electrical double-layer model for sorption of ions on octade-cylsilyl bonded phases including the role of residual silanol groups. Anal. Chem. 1991, 63, 993-1000. 

If the rate equations given above for heterogeneous mixtures are applied for the sorption of ions by soils or soil components, one has, of... 

Spurred by the work of Stumm (e.g., 11-13), surface complexation modeling has emerged as a powerful tool for describing chemical sorption of ions onto reactive mineral surfaces. In surface complexation models, ions and individual functional groups on the surface are considered to react to form... 

The phenomena presented in this book were discussed in many reviews. For example, Schwarz [13] discussed methods used to characterize the acid base properties of catalysts. The review on sorption on solid - aqueous solution interface by Parks [14] includes also principles of surface science. The book Environmental Chemistry of Aluminum edited by Sposito reviews the solution and surface chemistry of aluminum compounds. Chapter 3 [15] provides thermochemical data for aluminum compounds. Chapter 5 [16] lists the points of zero charge of aluminum oxides, oxohydroxides and hydroxides with many references on adsorption of metal cations and various anions on these materials. Unlike the present book, which is confined to sorption from solution at room temperature, publications on coprecipitation and adsorption from gas phase or at elevated temperatures are also cited there. Brown et al. [17] reviewed on dry and wet surface chemistry of metal oxides. Stumm [18] reviewed sorption of ions on iron and aluminum oxides. The review by Schindler and Stumm [19] is devoted to surface charging and specific adsorption on oxides. Schindler [19] published a review on similar topic in German. Many other reviews related to specific topics are cited in respective chapters. 

The pH effects on sorption of ions have been interpreted in terms of ... 

Barrow [772] derived a kinetic model for sorption of ions on soils. This model considers two steps adsorption on heterogeneous surface and diffusive penetration. Eight parameters were used to model sorption kinetics at constant temperature and another parameter (activation energy of diffusion) was necessary to model kinetics at variable T. Normal distribution of initial surface potential was used with its mean value and standard deviation as adjustable parameters. This surface potential was assumed to decrease linearly with the amount adsorbed and amount transferred to the interior (diffusion), and the proportionality factors were two other adjustable parameters. The other model parameters were sorption capacity, binding constant and one rate constant of reaction representing the adsorption, and diffusion coefficient of the adsorbate in tire solid. The results used to test the model cover a broad range of T (3-80°C) and reaction times (1-75 days with uptake steadily increasing). The pH was not recorded or controlled. 

The concentrations of the working solutions are related to the sensitivity of the spectrophotometric method 0.1 mg, 10 pg, or 1 pg of element per ml. Solutions of concentration 10 pg/ml, and especially 1 pg/ml, are prepared freshly on the day of use. The instability with time, observed in more dilute working solutions, is mainly due to sorption of ions on the surface of the vessel [83,84]. 

Sorption of Ions in Trace Amounts in the Presence of a Supporting Electrolyte... 

Several models have been developed to describe reactions between aqueous ions and solid surfaces. These models tend to fall into two categories (1) empirical partitioning models, such as distribution coefficients and isotherms (e.g., Langmuir and Freundlich isotherms), and (2) surface-complexation models (e.g., constant-capacitance, diffuse-layer, or triple-layer model) that are analogous to solution complexation with corrections for the electrostatic effects at the solid-solution interface (Davis and Kent, 1990). These models have been described in numerous articles (Westall and Hohl, 1980 Morel, Yeasted, and Westall, 1981 James and Parks, 1982 Barrow, 1983 Westall, 1986 Davis and Kent, 1990 Dzombak and Morel, 1990). Travis and Etnier (1981) provided a comprehensive review of the partitioning and kinetic models typically used to define sorption of ions by soils. The reader is referred to the cited articles for details of the models. 

An important consideration in constructing certain types of geochemical models, especially those applied to environmental problems, is to account for the sorption of ions from solution onto mineral surfaces. Metal oxides and aluminosilicate minerals, as well as other phases, can sorb electrolytes strongly because of their high reactivities and large surface areas (e.g., Davis and Kent, 1990). When a fluid comes in contact with minerals such as iron or aluminum oxides and zeolites, sorption may significantly diminish the mobility of dissolved components in solution, especially those present in minor amounts. 

It is evident that the shape of the impedance spectra varies with the potential since the values of the charge transfer resistance (Ret), the low frequency (redox) capacitance (Cl) and the Warburg coefficient change with the potential more exactly, they depend on the redox state of the polymer. In many cases D is also potential-dependent. The double-layer capacitance (Cdi) usually shows only slight changes with potential. The ohmic resistance (Rq) is the sum of the solution resistance and the film resistance, and the latter may also be a function of potential due to the potential-dependent electron conductivity, the sorption of ions, and the swelling of the film. In Fig. 3.9 three spectra are displayed, which were constructed using the data obtained for a PTCNQ electrode at three different potentials near its equilibrium potential [23]. 

AGs becomes positive, and so the sorption of ions in phase a is less likely. If we assrrme that this electrostatic interaction dominates, i.e., AGsoiv = AjU , and taking into account that (water) is 78 at 25 ° C while (organic phase) is usually less than 10, the activity (concentration) ratio shorrldbe very small. Of course, AjUj may also depend on the differences between other interactions (e.g., van der Waals interactions) in the two phases. 

Mechanism of Particle Detachment. The charging of adherent particles under the influence of a dc field may occur as a result of polarization of the particle material and sorption of ions on the particle surface [130]. In order to define more clearly the mechanism of particle detachment, certain experiments were performed on the measurement of particle charge and on surface cleaning in different gas media. 

The detachment of particles may be prevented by sorption of ions on the surface. The charge acquired by a particle as a result of ion sorption (see Fig. VII. 2.c) should be determined by the residence time of the particle in the high-voltage field. According to experimental results reported in [130], particles acquire a maximum charge after being held in the field of a corona discharge for 0.1 sec, or in an electrostatic field for 5-10 min. 

Fig. VI 1.2. Particle charging and charge sign reversal (a, b, c) exposed to steady electric field (d) exposed to alternating field (a) on insulator (b) on conductor (c) on conductor with sorption of ions.

In the preceding chapters, we revisited the interaction of ions with soil components, mainly minerals, and humic substances. As it should be apparent, there are a high number of studies on sorption of ions to soil components, and in many aspects, it is a field fairly well known. All these are laboratory studies, under well-controlled conditions. Now, the question arising is. How do we apply all these results to a natural soil, where the components are interacting between themselves, and the conditions are changing due to climate, human, and animal activity There is no easy answer to this question, and in fact, nowadays, we are rather far away from satisfactory results in this respect. In this chapter, we will try to reflect the state-of-the-art response to this problem. 

The sorption of ions in laboratory systems formed by a few (mainly two or three) soil components has received attention, albeit not very extensive, from several research gronps (note that here binary and ternary refer to the number of soil components in the literature, the term ternary often refers to two components plus one adsorbing ion). We will summarize here some important results. 

Fairly obviously, the sorption of ions is most efficient, i.e. most closely approaches the theoretical maximum, when each resin particle has time to take up as many ions as it is capable of retaining, i.e. when the flow is very slow. In practice, however, there is usually a time constraint on analyses, and a good compromise is to use a flow rate of 1 ml/min/cm of column cross-section. This permits practical exchange capacities not... 

Fig. X.5. Charging and discharging of the particles. a,b,c) On application of a steady electric field d) on application of an alternating field, a) On an insulator b) on a conductor c) on a conductor with the sorption of ions.

In our experiments the dust-laden surface was held in an electric field for more than 10 min, so that the sorption of ions on the surface may be expected to have taken place. 

Unlike porous amorphous carbons, the high ratio of the external surface area to the total surface area of CNTs provides fast adsorption/desorption of electrolyte ions associated with the process of the formation of the electric double layer due to no ion-sieving effect occurring (Arulepp et al. 2006). Sorption of ions onto external surface area of CNTs makes the double-layer capacitance of CNT-based actuators less dependent on the ionic hquid species (ion dimensions) than the capacitance of amorphous carbon-based actuators, where the ion transport into the pores depends on the pore size and the size of electrolyte ions. The frequency dependence of generated strain has been attributed to the elecfrochemical kinetics different deflection amplitudes are the result of different ionic conductivities of EL species (Imaizumi et al. 2012). 

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