Ion exchange, simple

Adsorption of a dissolved ionic species is always part of an exchange reaction that involves a competing ionic species. The desorbing species creates the vacant site to be occupied by the adsorbing one. Soil scientists use a variety of ion exchange models (e.g., the Gaines-Thomas, Gapon, Vanselow, and Rothmund-Kornfeld models) in which different conventions are used to write the concentrations of dissolved and adsorbed species. These models are adequately described and compared elsewhere (cf. Bolt 1979 Sposito 1981, 1989 Appelo and Postma 1993). 

It is likely that the adsorption sites on most solids are monovalent (Jenne 1995). Nevertheless, to avoid having to write fractional moles of divalent cations, sorption sites are assumed divalent in the following discussion. Thus, in the above example, where Na competes with Cd for sorption sites on the montmorillonite, the competitive reaction is written 

How can one deal with the activities of species in the equilibrium expression for ion exchange For the aqueous ions we can often use the Debye-Huckel or Davies equation to obtain ion activity 

The value of D may be relatively constant for exchange reactions involving major concentrations of ions and sorbents such as smectite clays or zeolites (cf. Langmuir 1981). However, D for exchange reactions between major and trace constituents can change by orders of magnitude as their concentrations change. 

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Little more need be said here about the simple ion-exchange reactions such as that between sodium hexametaphosphate and calcium ions (Scheme 10.7). It is useful, however, to consider in more detail those reactions involving chelation (Scheme 10.8). This is a reversible reaction, the equilibrium being dependent on the process pH and the concentrations of the reacting species (Equation 10.2). While chelated complexes are less stable at higher temperatures, this effect can be ignored in practice. The factors involved have been discussed in some considerable detail by Engbers and Dierkes [20,23]. 

Procedure As Phleum pretense produces much more pollen thanElieracium species and previous work, I have focused my limited efforts in this area of research on P. pratense. The author still uses simple ion-exchange chromatography to extract pigments and in P. pratense, most of these are flavonoids. 

Cations other than Li+ can be introduced into the film by a simple ion-exchange procedure, and this may be a simple method for obtaining multilayered structures with any cation. Organic cations, e.g., cyanine dyes, can also be introduced into the film by this procedure. Perhaps this approach for the application of highly ordered thin LB films onto the surface of electrodes could yield some new results, such an improvement in response time, as was discussed in Section 7.3.7. 

Sibbesen E. A simple ion-exchange resin procedure for extracting plant available elements from soil. Plant Soil 1977 46 665-670. 

In the phase transfer polymerization reactions, if one assumes a simple ion exchange at the interface (liquid-liquid or solid-liquid) ( ) (Equation 4)... 

Synthetic fluor-containing apatites are prepared and investigated for biomedical applications and serve also as models to understand the formation of biological fluorapatites and some of their properties. The synthesis of fluoridated apatites has been accomplished in various ways from simple ion exchange in solution to more elaborate techniques involving sol-gel routes or thermal processes. Two main classes of synthesis routes are presented in this chapter high-temperature routes and low-temperature solution routes. 

It occurred to us that ionic interactions might be a highly suitable binding motif to enforce the formation of heterobidentate ligand combinations [48[. The assembly ligand 14 /IS has been formed from the well-known TPPMS (14, monosulfonated triphenylphosphine sodium salt) and 3-(diphcnylphosphinyl)aniline hydrochloride (IS) by a simple ion-exchange reaction (Scheme 10.6). The coordination behavior ofthe ion-pair 14 /I S has been tested with various transition metal complexes. Other... 

In the extraction process, the aurocyanide complex plus other metal cyanide complexes that are common in cyanide leach liquors (e.g. Fe(CN) 4-, Fe(CN)63-, Zn(CN)42-, Ni(CN)42-, Cu(CN)43-and Co(CN)63-) load onto the resin by simple ion exchange ... 

Alternative approaches have been proposed over the years. In none of these cases is there sufficient experimental evidence for truly heterogeneous catalysis. Frechet et al. (55) used a polyvinylpyridinium (PVP) material for supporting chlorochromate [Cr(IV)02Cl ] or dichromate [CrCVI Oy-]. Cr3+ can be immobilized by simple ion exchange on polymers such as Nation or on a Y zeolite (59, 60). However, it is doubtful whether these methods ensure complete Cr anchoring when the material is brought into contact with oxidants. Clark et al. (61) advocated the use of alumina-anchored dichromate. Particularly when a neutral alumina is used, surface-anchored species are formed ... 

To optimize the use of the amorphous sodium titanate powders as catalyst substrates, it is important to fully characterize the ion-exchange properties of the material. Further, the solution properties of the active metal to be loaded onto the support will be an important parameter in the control of the adsorption process. For example, exposure of sodium titanate to a nickel salt solution does not guarantee that nickel will be loaded onto the sodium titanate, or that the nickel, if loaded, will be dispersed on an atomic level. Sodium titanate only behaves as a cation exchange material under certain pH conditions. The solution pH also influences the hydrolysis and speciation of dissolved nickel ions (3), which can form large polymeric clusters or colloidal particles which are not adsorbed by the sodium titanate via a simple ion-exchange process. 

As elucidated from the adsorption experiment on BSA, adsorption of gallium ion by simple ion-exchange effect is negligible. The characteristics of metal ions such as ionic radius and hardness/softness, and the conformation of the metallothionein probably affect the selectivity of metal adsorption. The understanding of the mutual interactions among those factors would be a key dictor in designing the protein-based ligand suitable for a specific metal ion. 

The catalysts preparable with swelling layer lattice silicates are classified into four types, as illustrated in Fig. 1. The intercalate of hydrated metal ion (a. Fig. 1) is easily obtained by a simple ion-exchange reaction in an aqueous medium. The intercalate acts as a Br0nsted acid catalyst because... 

A third class of ion-selective carriers consists of so-called charged carriers or associated ion exchangers. Unlike the simple ion exchangers, however, the selectivity of charged carriers is dictated by the degree of association of the analyte ion with the carrier as well as the partitioning of the analyte into the membrane... 

Haia, N., Matsumura, Y. Simple ion-exchange thin-layer chromatographic technique for the determination of traces of metals Kogyo Kagaku Zasshi 74, 364 (1971) C. A. 74,... 

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