Cation exchanger exchange reactions

A.cidic Extractants. Acidic extractants, HE, react with REE according to a cation-exchange reaction ... 

Formation damage caused by clay migration may be observed when the injected brine replaces the connate water during operations such as water-flooding, chemical flooding including alkaline, and surfactant and polymer processes. These effects can be predicted by a physicochemical flow model based on cationic exchange reactions when the salinity decreases [1665]. Other models have also been presented [345,1245]. 

The selectivity of an ion-exchange resin means its ability to discriminate among different ionic species. A cation-exchange reaction can be represented by an equation of the form... 

Mineral colloid-enzyme interactions have been documented (e.g., Theng 1979 Bums 1986 Naidja et al. 2000 Bums and Dick 2002). Besides cation-exchange reactions, adsorption of enzymes by mineral colloids may proceed through ionic, covalent, hydrophobic, hydrogen bonding, and van der Waals forces. When enzymes are adsorbed on mineral colloids, changes in the tertiary structures (i.e., the folding of the helix or... 

Several chemical geothermometers are in widespread use. The silica geothermometer (Fournier and Rowe, 1966) works because the solubilities of the various silica minerals (e.g., quartz and chalcedony, Si02) increase monotonically with temperature. The concentration of dissolved silica, therefore, defines a unique equilibrium temperature for each silica mineral. The Na-K (White, 1970) and Na-K-Ca (Fournier and Truesdell, 1973) geothermometers take advantage of the fact that the equilibrium points of cation exchange reactions among various minerals (principally, the feldspars) vary with temperature. 

The free gpergy change for the general cation exchange reaction between A and B cations on an exchanger X, represented by... 

The synthesis of ionic liquids with BF4 and PF6 as cations has been the subject of much research since they are the most widely used in catalysis. However, it is difficult to make these ionic liquids in a pure form. The original route used to prepare ionic liquids with these anions consists of a metathesis (anion-cation exchange) reaction in which the imidazolium chloride is reacted with the sodium salt of the anion in a suitable solvent [8], The reaction is illustrated in Scheme 4.2 for the tetrafluoroborate salt. 

The solutions of the metal compounds M3X7 can be used (a) for a study of redox-reactions under mild conditions, and (b) to serve as aducts for cation exchange reactions. Thus KaaPv reacts with phi PCl or phi AsCl accompanied by quantitative precipitation of KaCl, to give solutions of salts without metal cations. The least soluble materials which crystallize out of these solutions are the compounds (phi P)2Pie or (ph As)2Pie They contain the new polyanion Pie (Figure 5)> which is formed in the solution by a complex redox reaction (J 8). 

Acidic extractants that undergo a cationic exchange reaction with metal ions do not generally require equilibration before extraction, because the exchange involves protons that are already present in the extractant ... 

Base cations are mobilized by weathering and cation exchange reactions that neutralize acids in the watershed. They respond therefore indirectly to changes in sulphate and nitrate concentrations. In fact, if acid anion concentrations (mainly sulphate) decrease, base cations are also expected to decrease. However, in the last few years an increase of the occurrence of alkaline rain episodes (probably due to climatic effects) has been observed and it is likely that calcareous Saharan dust, rich in base cations, is responsible for it [27]. Accelerated weathering, resulting from recent climate warming may also contribute to higher base cation concentrations [28]. 

Comments and reported properties prepared by cation-exchange reactions,... 

The ion-exchange mechanism of exfracfion does nof occur only for amino acids. We observed if also for cafecholamines [26]. These compounds are efficiently extracted into ILs in the cationic form, af pH 1-8. Af fhese pH, the primary (dopamine) or secondary (adrenaline and dobutamine) amino groups are protonated (catecholamines are oxidized in alkaline solutions at pH > 8). By analogy with amino acids, extraction may be described by the cation-exchange reaction ... 

Applying the foregoing thermodynamic and kinetic information to manganese behavior in natural water systems is considerably limited because the manganese system exemplifies the difficulties discussed earlier. On the thermodynamic side, the kinds of oxide phases in natural waters may not correspond to those for which equilibrium data are available. Also, cation exchange reactions are probably important (21). On the kinetic side, the role of catalysis by various mineral surfaces in suspension or in sediments is not really known. Of considerable importance may be microbial catalysis of the oxidation or reduction processes, as described by Ehrlich (7). With respect to the real systems, relatively... 

CHEMICAL THERMODYNAMICS OF CATION EXCHANGE REACTIONS THEORETICAL AND PRACTICAL CONSIDERATIONS... 

The general cation exchange reaction in a binary exchange system can be expressed as (Sposito, 1986) ... 

Equation (5.40) is expected whenever iq and v x depend on powers of the concentrations of the reactants and products in Eq. (5.36), and the power exponents are the stoichiometric coefficients of the four species involved (Denbigh, 1981). Even if Eq. (5.37) is simplified in this way, the assumption must be made that the mechanism of the cation exchange reaction at equilibrium does not change when vl f v j so that finite rate data can be used to apply Eq. (5.40). 

The reactions in Eqs. 5.1 and 5.2, taken in the broadest geochemical sense, refer only to the replacement of one ion by another existing in a solid structure. Thus, for example, Eq. 5.1 could be applied to provide a description of solid solution composition alternate to that in Section 3.3. Instead of basing the composition of Al-goethiteon the solid components diaspore and goethite, as in Eq. 3.41, one could describe a continuum of possible compositions by combining Eqs. 3.39a and 3.39b into the cation exchange reaction... 

Exchange isotherms can be used to calculate an exchange selectivity coefficient, the conventional terminology for the conditional equilibrium constant associated with Eq. 5.1 or 5.2. For example, in the case of the cation exchange reaction in Eq. 5.1,... 

Another kind of experimental consistency check with Eq. 5.25 can be made if Kei is determined for three or more binary exchange reactions. Consider, for example, the three following cation exchange reactions ... 

Equation 5.31 provides the basis for a test of both experimental precision and thermodynamic self-consistency when the ArG° values are calculated using values of In Kex determined with the help of Eq. 5.25c. Table 5.2 shows some typical examples of this test applied to cation exchange reactions on three montmoril-lonites.12 The values of b ArG°(3) expected according to Eq. 5.31b are given in the eighth column of the table. In each case the measured value of b ArG°(3) in column 7 is in fair agreement with the theoretical value based on the requirement of self-consistency, the mean deviation between measured and theoretical values being +0.62 kj mol ]. 

Table 5.2 Consistency Tests According to Eq. 5.31b for Cation Exchange Reactions on Three Montmorillonites. (ArG° values in kJ mol"1)...

For each additional exchanging ion, one simply adds a term, X d In fi with the understanding that the sum of the mole fractions Xj (i = 1, 2, 3,. . . ) must always equal 1.0. Similarly, for each possible cation exchange reaction (Eq. 5.1), one defines a conditional exchange equilibrium constant... 

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