Exchange phenomena, cation

Most previous adsorption studies employing calorimetry have investigated cation exchange phenomena on zirconium phosphates (17-21), titanium phosphate (22) and clay minerals (23,24). 

Table 2), which adequately reflects the anion sorptivity of the models. To take into account the different role of clay mineral and organic matter in cation exchange phenomena, acidity titration was performed in 1 N CaCb and KCl solutions. In fact, it is well known that organic matter hinds Ca more strongly than K ions, whereas 2 1 clay minerals such as bentonite are more selective for K than Ca ions [25]. As a consequence, the presence of favored the exchange of the clay-sorbed and interlayer Al- or Fe-, while the presence of Ca destabilized the organically-bound Al- and Fe-. 

The petrophysical origin of the IP effects is connected with electrochemical processes of the electronic-ionic interaction, interface properties at the grain-fluid boundary region, cation exchange phenomenon, pore constrictivity, and other effects controlled by rock components, their distribution, and interaction (Fig. 8.38). 

Electrochemical studies, in combination with EPR measurements, of the analogous non-chiral occluded (salen)Mn complex in Y zeoUte showed that only a small proportion of the complex, i.e., that located on the outer part of the support, is accessible and takes part in the catalytic process [26]. Only this proportion (about 20%) is finally oxidized to Mn and hence the amount of catalyst is much lower than expected. This phenomenon explains the low catalytic activity of this system. We have considered other attempts at this approach using zeolites with larger pore sizes as examples of cationic exchange and these have been included in Sect. 3.2.3. 

Another type of reaction that responds to WD cycles is the fixation of K and NH4 ions by smectite (3-7). The fixation of K in smectite has been studied extensively by soil scientists because of its effect on the availability of plant nutrients. The reaction also decreases smectite s ability to swell, decreases its cation exchange capacity (CEC), and modifies its BrjSnsted acidity. Therefore, an understanding of this phenomenon is applicable to many fields of study that are concerned with swelling clays, fields such as soil fertility, soil mechanics, waste disposal, clay catalysis, and the geochemistry of ground and surface waters. 

Figueras et al. (105) found some direct evidence for electron-deficient palladium clusters on various cation-exchanged forms of zeolite Y from CO adsorption experiments. In particular, a correlation was observed between the turnover number for benzene hydrogenation and the CO stretching frequency. The shift toward higher frequency with increasing support acidity was considered as evidence for increased electron acceptor properties of the support. Further studies will, however, be required to provide a more detailed understanding of this phenomenon. 

An interesting (if not fully understood) phenomenon has been observed by Smith et al. as strong cation-exchange (SCX) phases were used to separate tricyclic antidepressants [47], A certain focusing effect, which is not reproducible, produced peaks of staggering efficiencies, millions of plates per meter, the... 

A similar phenomenon was observed upon the exchange of Cs and Rb with sulfophenolic cation exchanger in alkaline solution [36, p. 172]. 

In order to examine more completely the above phenomenon, experiments have been carried out with both an anion and cation exchanger [14]. The resin phase chloride ion concentration levels were provided by equilibrating the AG 1-X4 with 1.84 M HCl and the Dowex 50 W-X4 with 5.4 M HCl, respectively. To obtain the resin phase absorption spectra for study, both resins were equilibrated with a 2.64 M HCl solution containing cobalt. The absorption spectra are essentially duplicated in the two exchangers (Fig 4). Once again the sizable presence of CoClj or CoCl ... 

Titanium, as an example for the transport model verification, was chosen because of the extensive experimental data available on LLX and membrane separation [1,2,74—76] and of its extraction double-maximum acidity dependence phenomenon [74]. This behavior was observed for most extractant families basic (anion exchangers), neutral (complexants), and acidic (cation exchangers). So, it is possible to study both counter- and cotransport mechanisms at pH > 0.5 and [H] > 7 mol/kg feed solution acidities, respectively, using neutral (hydrophobic, hydrophilic) and ion-exchange membranes. 

The phenomenon of ion exchange was observed and scientifically documented for the first time by Way and Thompson in 1850. They confirmed the ion-exchange properties of soils and simulated the following naturally occurring cation-exchange reactions for... 

It is fortunate for humans that the phenomenon of cation exchange capacity exists. Without this... 

It would be appropriate, at least from a mechanistic or "first principles standpoint, to possess a theoretical molecular-based analysis of this equilibrium, including internal water content hydration effects. The remaining discussion of this topic is concerned with the efforts of Mauritz, et jal., in providing a fundamental molecular representation of the phenomenon of ion-pairing and subsequently relate this model to the swelling of membranes in specific cation-exchanged salt forms. 

The phenomenon of ion exchange is thought to be the oldest physical process known to man, dating back to descriptions in the Bible and the writings of Aristotle. It was also the first property of zeolites to be studied scientifically when, in 1858, Iiichom [1] showed that the natural zeolites chabazite and natrolite were capable of reversible cation exchange. 

Hydrolysis increases as the aluminium content of the zeolite in contact with the water increases, so the cation exchange becomes ternary rather than binary. This phenomenon can be easily confirmed by monitoring the pH of water in contact with a zeolite. The initial high value (pH 10) drops as reaction (17) proceeds. Examples of this are seen in Harjulaet al. [32] Other secondary reactions now arise ... 

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