Kinetics and Thermodynamics of Ion Exchange on Amorphous Iron (III) Antimonate in Mixed Solvents

A research program on ion exchange of the acidic salts of multivalent metals in aqueous and mixed media has been initiated with the aim of elucidating their ion exchange behaviour and selectivity phenomena in general. To achieve this goal, the kinetic and thermodynamic cation exchange behaviour of cerium(IV) and tin(IV) antimonates in aqueous solutions have been previously examined. Comparison of the results obtained with other results for other metals antimonates (particularly iron(III) antimonate), has led to some useful conclusions regarding the selectivity behaviour and the ion exchange kinetics of the acidic salts of multivalent metals and has also emphasized the major role of the acidity of the exchange sites in determining the selectivity. The present work reports on the kinetics and thermodynamics of exchange on iron(III) antimonate in aqueous solution and in the presence of up to 90% (w/w) acetone, methanol and isopropanol. The results obtained are compared with those on the other inorganic exchangers and organic resins. The results showed that the effective diffusion coefficients of Na+ and Cs+ decrease with the increase of solvent concentrations in solution and Di is lower than in aqueous solutions.The values of activation energies of cation diffusion process in mixed solvent are higher compared with the cation diffusion in aqueous solutions. This may be due to the higher basicity of the alcoholic solutions that increases the acidity of the exchange sites of the matrices. The selectivity series for H+/Na+ and H+/Cs+ exchange on FeSb increases in the order, aqueous < methanol for Na+ and aqueous < methanol < acetone < isopropanol for Cs+. (Authors)