Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

The Adsorption of Ions

Efficiency The effectiveness of the operational performance of an ion ex- changer. Efficiency in the adsorption of ions is expressed as the quantity of regenerant required to effect the removal of a specified unit weight of adsorbed material, for example, pounds of acid per kilogram of salt removed. [Pg.437]

The adsorption of ions due to an electrified interface can be evaluated by considering a series of laminae of the solution at various distances from the metal surface and assessing the number of ions present as compared with those that would have been present if the electrified interface had been... [Pg.1175]

Figure 7.15 shows the adsorption of ion exchangers, downflow pattern. The bed has an adsorption zone with respect to time and is saturated with solute. [Pg.186]

Many precipitates, such as Fe(OH)3, form initially as colloidal suspensions. The tiny particles are kept from settling out by Brownian motion, the motion of small particles resulting from constant bombardment by solvent molecules. The sol is further stabilized by the adsorption of ions on the surfaces of the particles. The ions attract a layer of water molecules that prevents the particles from adhering to one another. [Pg.464]

In situ infrared spectroscopy allows one to obtain stracture-specific information at the electrode-solution interface. It is particularly useful in the study of electrocat-alytic reactions, molecular adsorption, and the adsorption of ions at metal surfaces. [Pg.505]

In the case of the adsorption of ions, the adsorption free energy is proportional to the excess surface charge density [37],... [Pg.126]

Capacitance and surface tension measurements have provided a wealth of data about the adsorption of ions and molecules at electrified liquid-liquid interfaces. In order to reach an understanding on the molecular level, suitable microscopic models have had to be considered. Interpretation of the capacitance measurements has been often complicated by various instrumental artifacts. Nevertheless, the results of both experimental approaches represent the reference basis for the application of other techniques of surface analysis. [Pg.439]

It is assumed that the quantity Cc is not a function of the electrolyte concentration c, and changes only with the charge cr, while Cd depends both on o and on c, according to the diffuse layer theory (see below). The validity of this relationship is a necessary condition for the case where the adsorption of ions in the double layer is purely electrostatic in nature. Experiments have demonstrated that the concept of the electrical double layer without specific adsorption is applicable to a very limited number of systems. Specific adsorption apparently does not occur in LiF, NaF and KF solutions (except at high concentrations, where anomalous phenomena occur). At potentials that are appropriately more negative than Epzc, where adsorption of anions is absent, no specific adsorption occurs for the salts of... [Pg.224]

The adsorption of ions is determined by the potential of the inner Helmholtz plane 0n while the shift of Epzc to more negative values with increasing concentration of adsorbed anions is identical with the shift in 0(m). Thus, the electrocapillary maximum is shifted to more negative values on an increase in the anion concentration more rapidly than would follow from earlier theories based on concepts of a continuously distributed charge of adsorbed anions over the electrode surface (Stern, 1925). Under Stern s assumption, it would hold that 0(m) = 0X (where, of course, 0X no longer has the significance of the potential at the inner Helmholtz plane). [Pg.233]

The adsorption of ions at insulator surfaces or ionization of surface groups can lead to the formation of an electrical double layer with the diffuse layer present in solution. The ions contained in the diffuse layer are mobile while the layer of adsorbed ions is immobile. The presence of this mobile space charge is the source of the electrokinetic phenomena.t Electrokinetic phenomena are typical for insulator systems or for a poorly conductive electrolyte containing a suspension or an emulsion, but they can also occur at metal-electrolyte solution interfaces. [Pg.253]

As the membrane has a surface charge leading to formation of a diffuse electrical layer, the adsorption of ions on the BLM is affected by the potential difference in the diffuse layer on both outer sides of the membrane 02 (the term surface potential is often used for this value in biophysics). Figure 6.12 depicts the distribution of the electric potential in the membrane and its vicinity. It will be assumed that the concentration c of the transferred univalent cation is identical on both sides of the membrane and that adsorption obeys a linear isotherm. Its velocity on the p side of the membrane (see scheme 6.1.1) is then... [Pg.454]

Figure 3.23 The charge on a colloid. The charge carried by a colloid because of its chemical composition and the pH of the solution (the electrochemical potential) is reduced by the adsorption of ions from the solution and the resulting charge is known as the zeta potential. Figure 3.23 The charge on a colloid. The charge carried by a colloid because of its chemical composition and the pH of the solution (the electrochemical potential) is reduced by the adsorption of ions from the solution and the resulting charge is known as the zeta potential.
Ruth et alS4-7) have made measurements on the flow in a filter cake and have concluded that the resistance is somewhat greater than that indicated by equation 7.1. It was assumed that part of the pore space is rendered ineffective for the flow of filtrate because of the adsorption of ions on the surface of the particles. This is not borne out by Grace18 or by Hoffing and Lockhart(9) who determined the relation between flowrate and pressure difference, both by means of permeability tests on a fixed bed and by filtration tests using suspensions of quartz and diatomaceous earth. [Pg.377]

In electrochemistry, the electrode current is conventionaUy classified into the faradaic current and the nonfaradaic current. The former is the electric current associated with charge transfer reactions at nonpolarizable electrodes and the latter is the current that is required to establish the electrostatic equilibrium at the interfacial double layer on both polarizable and nonpolarizable electrodes. The nonfaradaic ciurent, sometimes called a transient current, flows also in the course of establishing the adsorption of ions on electrodes. [Pg.90]

This is true only in dilute solutions, because at high ionic strengths, the adsorption of ions alters the mineralogy of the solid s surface, thereby affecting its activity. [Pg.131]

The adsorption of ions on iron oxides regulates the mobility of species in various parts of the ecosystem (biota, soils, rivers, lakes, oceans) and thereby their transport betv een these parts. Examples are the uptake of plant nutrients from soil and the movement of pesticides and other pollutants from soils into aquatic systems. In such environments various ions often compete with each other for adsorption sites. Adsorption is the essential precursor of metal substitution (see Chap. 3), dissolution reactions (see Chap. 12) and many interconversions (see Chap. 14). It also has a role in the synthesis of iron oxides and in crystal growth. In industry, adsorption on iron oxides is of relevance to flotation processes, water pollution control and waste and anticorrosion treatments. [Pg.253]

The electrical double-layer (edl) properties pose a fundamental problem for electrochemistry because the rate and mechanism of electrochemical reactions depend on the structure of the metal-electrolyte interface. The theoretical analysis of edl structures of the solid metal electrodes is more complicated in comparison with that of liquid metal and alloys. One of the reasons is the difference in the properties of the individual faces of the metal and the influence of various defects of the surface [1]. Electrical doublelayer properties of solid polycrystalline cadmium (pc-Cd) electrodes have been studied for several decades. The dependence of these properties on temperature and electrode roughness, and the adsorption of ions and organic molecules on Cd, which were studied in aqueous and organic solvents and described in many works, were reviewed by Trasatti and Lust [2]. [Pg.768]

H. Eichorn Proved that the adsorption of ions by clays and zeolites constitutes a reversible reaction. 1858... [Pg.40]

Lateral Interactions. Besides the forces between the metal and the adsorbate, forces between the adsorbed molecules may exist and they may welcome or reject the adsorbing ion. To understand them, consider the adsorption of ions on a surface electrode. Now choose one of those ions and consider it as a reference ion. Since the ions adsorbed around the reference ion carry the same charge as the reference ion, electrostatic repulsion forces emerge between the reference ion and its neighbors (Fig. 6.92). These interactions are of long range, and they decay as 1/r. [Pg.207]

Some Isotherms Used In Describing the Adsorption of Ions... [Pg.226]

We have studied the forces and parameters related to the adsorption of ions. We have gained knowledge of the different interactions involved in the contact adsorption process. Now it is time to return and look again at the experimental capacitance curves and try to explain them via the new knowledge we have gained about the interphasial structure. [Pg.242]

In these sections we learned about the processes and forces involved in the adsorption of ions from solution on electrodes, which can be represented by... [Pg.246]

The next step was to quantitatively determine some of the parameters involved in the adsorption of ions. We started by comparing equations of states in three dimensions (gas in a cylinder) with those in two dimensions (adsorbed molecules) (Section 6.8.5). This led us to define adsorption isotherms in electrochemical systems They are relationships relating the physical quantities [number of adsorbed molecules (r or 0), activity of ions in solution (a), charge or potential of the electrode ( M or E) and... [Pg.247]

Correspondingly, the forces involved in the adsorption of organic molecules can be classified into three categories organic molecule-electrode forces, water-electrode forces, and lateral interactions. These forces are the same as those we studied in the adsorption of ions on electrodes, and their nature was described in Section 6.8.2. [Pg.255]

The great sensitivity of ellipsometiy allows it to measure films down to a thickness of 0.1 monolayer, with possibilities of even greater sensitivity in sight Such measurements can be applied not only to thickness but also to the examination of the adsorption of ions and organic molecules on the surface of metals (see Fig. 7.58). [Pg.432]

The kinetics by which UPD layers form are qualitatively the processes already discussed. There are the electron transfer kinetics from the metal substrate to the depositing ion and the surface diffusion of the adions formed to edge sites on terraces. Complications occur, however, for there is the adsorption of ions to take care of and that brings up questions of which isotherm to use (Section 6.8). Three kinds of UPD formations are shown in Fig. 7.146. Thus Fig. 7.146 (c) shows ID phase formation along a monatomic step in the terraces on the single ciystal Fig. 7.146 (b) shows 2D nucleation at a step, and Fig. 7.146 (a) shows 2D nucleation on an atomically flat plane. [Pg.599]

Once the dirty spot is removed from the substrate being laundered, it is important that it not be redeposited. Solubilization of the detached material in micelles of surfactant has been proposed as one mechanism that contributes to preventing the redeposition of foreign matter. Any process that promotes the stability of the detached dirt particles in the dispersed form will also facilitate this. We see in Chapter 11 how electrostatic effects promote colloidal stability. The adsorption of ions —especially amphipathic surfactant ions —onto the detached matter assists in blocking redeposition by stabilizing the dispersed particles. Materials such as carbox-ymethylcellulose are often added to washing preparations since these molecules also adsorb on the detached dirt particles and interfere with their redeposition. [Pg.340]

To arrive at an understanding of the distribution of charge and potential near an interface, it is helpful to consider an electrode. A reversible electrode is one in which each of the phases contains a common ion that is free to cross the interface. The system Ag-Agl-aqueous solution is an example of a reversible electrode. A polarizable electrode, on the other hand, is impermeable to charge carriers, although charge may be brought to the surface by the application of an external potential. The system metallic Hg-aqueous solution is an example of a polarizable electrode we discussed the relationship among the applied potential, the interfacial tension, and the adsorption of ions in Chapter 7, Section 7.11. [Pg.503]

Previous studies of the adsorption of ions on montmorillonite have emphasized low salt concentration regions (see, e.g. ref. 1-11). Our main interest is in higher salt concentrations, because many of the brines in oil reservoirs are in this range, and because some favored locations for nuclear waste disposal, bedded salt deposits and salt domes, may result in high ionic strength environments. [Pg.298]


See other pages where The Adsorption of Ions is mentioned: [Pg.103]    [Pg.803]    [Pg.812]    [Pg.1175]    [Pg.115]    [Pg.774]    [Pg.73]    [Pg.22]    [Pg.368]    [Pg.49]    [Pg.274]    [Pg.40]    [Pg.185]    [Pg.219]    [Pg.254]    [Pg.947]    [Pg.85]    [Pg.16]    [Pg.333]    [Pg.287]    [Pg.169]   


SEARCH



Adsorption of ions

Ion adsorption

© 2024 chempedia.info