Ion-Exchange Equilibria for [Au(CN)₂]^-/Cl^-, [Au(CN)₂]^-/SCN^-, and SCN^-/Cl^- in Acetone + Water Mixtures at 303 K

Abstract

Ion-exchange equilibria are presented for [Au(CN) 2 ] -/Cl -, [Au(CN) 2 ] -/SCN -, and SCN -/Clin acetone + water mixtures at 303 K using Purolite A500 as the ion exchanger. The effect of the composition of acetone in the external solution on the ion-exchange isotherm for each binary system is considered. The experimental data are correlated using the law of mass action, modified with activity coefficients, to determine the equilibrium constant for each binary system. It is shown that the selectivity of Purolite A500 is highly dependent on the composition of the external solution. The selectivity of the resin for [Au(CN) 2 ] -, in particular, decreases markedly with an increase in the composition of acetone. The fitted values of the equilibrium constants are consistent with the trends observed in the corresponding ionexchange isotherms.

Revised Ion Exchange Method for Estimation of Conditional Stability Constants of Metal−Dendrimer Complexes

“…In recent years, equilibrium models based on the mass action law have also been employed to model ion exchange equilibria. , However, for this study, the classical Langmuir model appears more advantageous than mass-action-based models for the following reasons: (1) the simple Langmuir model can adequately interpret the isotherm data as shown in Figure and is much more straightforward in determining the model parameters as well as in model uses, and (2) while mass-action-based models require knowledge of solution and resin phase activity coefficients, the validity of classical methods (e.g., the Debye−Hückel equation) for determining the ionic strength in the presence of dendrimers is yet to be substantiated.…”

Ion-Exchange Equilibria for [Au(CN)2]-/Cl- and [Au(CN)2]-/SCN- on Purolite A500 in Mixed Solvents at 303 K

“…Ion-exchange equilibria were determined using a batch experimental method. A detailed description of the apparatus and procedure has been presented in earlier work on ion-exchange equilibria in aqueous solution . A 5-mL sample of the resin (wet and settled volume in water) was repeatedly contacted with 100 mL of a mixed-solvent stock solution containing a fixed concentration of the loading anion.…”

“…This semiempirical approach is often used to estimate the mean ionic activity coefficients, which are measurable. Values of a i pertinent to this study are given elsewhere . The Debye−Hückel parameters appearing in eq 6 ( A and B ) are equivalent to those in the corresponding equation for the mean ionic activity coefficient and are dependent on temperature ( T ) and the dielectric constant (ε) of the solvent .…”

“…If this is not the case, then K AB has a tendency to be underestimated. In addition, the two-parameter regression does not necessarily produce more-accurate results than the three-parameter regression . In view of the limited range of resin-phase composition in some of the mixed solvent systems, this method was not applied in this work.…”

“…The principle means of assessing the selectivity of the resin for a given species is through the measurement of binary ion exchange equilibria. We have previously reported binary ion-exchange equilibria for [Au(CN) 2 ] - /Cl - , and [Au(CN) 2 ] - /SCN - in aqueous solution using commercially available Purolite A500 as the ion-exchanger . In this work, binary ion-exchange equilibria are presented for the same systems in DMSO−water and NMP−water mixtures over a wide range of solvent composition.…”