Equilibrium metal cation exchange

A 0.5-gram mass of either the organo-treated or inorganic cation exchanged zeolite and 50 mL of 10 mM/L arsenate or chromate aqueous solutions were placed into Erlenmeyer flasks and mechanically shaken in reciprocating mode to attain equilibrium. Different equilibrium periods for individual zeolite modifications and both aqueous oxyanions species have been established. The adsorption isotherm experiments were conducted using above mass/ volume ratio of samples with an initial metal concentrations ranged from 0.5 to 100 mM/L at laboratory temperature. The... 

Exchange of complex cations. Complexation of transition metal cations with uncharged ligands such as with amines and with amino acids results in a selectivity enhancement compared to the selectivity of the aqueous metal cation (27, 65-72). Fig. 3 shows an example for the Cu(ethylenediamine) adsorption in montmorillonites of different charge density. Standard thermodynamic data for other cases are given in table IV. In all cases the free ligand concentration in equilibrium solution was... 

The equilibrium speciation of a metal ion influenced by cation exchange is dependent on the relative concentrations of the cations competing for the negatively charged sites on the particle s surface and their relative affinities for adsorption. Since one cation displaces another from the negatively charged sites, this process is termed cation exchange. 

The foundation of equilibrium-selective adsorption is based on differences in the equilibrium selectivity of the various adsorbates with the adsorbent While all the adsorbates have access to the adsorbent sites, the specific adsorbate is selectively adsorbed based on differences in the adsorbate-adsorbent interaction. This in turn results in higher adsorbent selectivity for one component than the others. One important parameter that affects the equilibrium-selective adsorption mechanism is the interaction between the acidic sites of the zeolite and basic sites of the adsorbate. Specific physical properties of zeolites, such as framework structure, choice of exchanged metal cations, Si02/Al203 ratio and water content can be... 

One of the parameters in the broad class of equilibrium-selective adsorption mechanisms is the interaction between the acidic and basic sites of the adsorbent and the adsorbate. ZeoUtes can be ion-exchanged with a variety of metal cations... 

Ion-exchange equilibrium In most experiments described here, monovalent cationic dyes have been used. D/ and M/ denote the dye cation and the alkali metal cation in solution. Z stands for zeolite and Y describes the cation concentration inside the zeolite. For monovalent cations and dyes which occupy two unit cells in zeolite L (e.g., Py" or Ox+), we must use (Mr ),] to describe the state of a given... 

Exchangers that have been loaded with cations or anions can be regenerated by treatment with acid or alkali, respectively, since one is always dealing with an equilibrium reaction. Commercially available ion exchangers are frequently delivered in the form of salts so that before use they must be converted into the free acids or bases. Metal cations can also be directly exchanged with one another. 

Various procedures can be applied to effect ion exchange. The simplest method is to work batchwise whereby the exchanger is left in contact with a solution of the ions to be exchanged until equilibrium is reached. This method is applicable to those exchange reactions where the equilibrium is in favor of the desired product this can of course always be achieved by employing a sufficient excess of a cation exchanger in its acidic form to a metal salt solution. 

The equilibrium in equation (94) is generally defined as a mass-distribution ratio such as that shown above for cation-exchange resins (equation 93), and the position of the equilibrium is determined by the relative Concentration of the counter-ion ML/- and the co-ion X-. The nature of the quaternary amine has little effect on the equilibrium properties of the resin, and the chemistry of metal complex formation in aqueous solution is the dominant factor. 

The reversible190 exchange of alkyl chlorides with metal bromides in a two-phase system, under PTC, has been reported to depend on the nature of the metal cation and the concentration of the aqueous phase. Most effective bromide donors are lithium191 and calcium bromides192 particularly when applied in the presence of a small amount of water. Interestingly, both the equilibrium composition and the rate in the reaction of various alkali and alkali earth bromides with -octyl chloride catalyzed by tetra- -hexylammonium bromide are strongly dependent on the amount of water present in the system193,194. 

The hypsochromic shift of the longest absorption band on complexation in ethanol solution and the bathochromic shift in chloroform solution are explained as follows. The hypsochromic shift in ethanol is affected by the phenol dissociation equilibrium (Eq. (1) in Scheme 2), the ion-exchange equilibrium, and the interaction of phenolate anion-metal cation [Eq. (2)]. In facts, the observed shifts depend upon the cation species, the amount of added salts, the reaction time, and, in some case, the counter anion species. 

Use of Eq. (18) permits identification of the log(y +/Yp,+ ) term as the one contributing most importantly to differences in affinity of pairs of univalent metal ions, M and N, for a cation-exchange resin. For example, for the equilibrium distribution of Li and Na ions between dilute solutions of Li and Na" " chloride (myQ + m jci = 0.010 m) and the much more highly concentrated Dowex-50 (8% cross-linked by weight with divinylbenzene) phase (niy, + iUnj, = 4.5 m) the p(Vy+ - Vjjj,+ )/2.3 RT and the 2 log(yyQ/y j(-i) term yield a small sum (< 0.04) while the value of log (Yu /Ynj,+ ) approaches 0.35 once correction for interaction between the two metal ions is made. Correlation between experiment and computation of the Gibbs-Donnan-based terms is strongly supportive of the model. 

D—H carbons are established very quickly there is hardly any difference between the first and subsequent cycles. For D—Ox carbon the anodic peak during the first 2 h of cycling decreased in size (Fig. 49) and correlated well with the silver adsorption equilibrium on this carbon. Nearly 40% of the adsorbed silver can be removed from this carbon surface with diluted acid (Table 14), which indicates that the cation exchanger can be reactivated by reduction according to the seheme proposed by Jannakoudakis et al. for noble metal ions [303-306] ... 

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