Thermodynamics of ion exchange of trivalent Coiii or Criii complex with cerium(III) ions on cation exchange resin

Abstract

The thermodynamic values of ion exchange of [M(B)_n(H₂O)_6-n]³⁺[M = Co^III or Cr^III, B = NH₃, (ethylenediamine = en)/2, (1,3-diaminopropane = tn)/2, (1,2-diaminopropane = pn)/2 or urea, 0 < n < 6] with Ce³⁺ ions on Dowex 50W resin of 2, 8 or 16% divinylbenzene (DVB) content were determined from selectivity coefficient and heat of exchange measurements at 25°C. Further, the equivalent volumes of [M(B)_n(H₂O)_6-n]³⁺-form resins of 2% DVB content were measured. The heat and entropy of exchange were negative for the preferential uptake of [MB₆]³⁺ by Ce³⁺-form resin of 2% DVB content and they vary significantly with the ligand, B. The sequence of their values was as follows: [Cr(urea)₆]³⁺ < [Co(NH₃)₆]³⁺≈[Cr(NH₃)₆]³⁺ < [Co(en)₃]³⁺ < [Co(tn)₃]³⁺≈[Co(pn)₃]³⁺. From the entropy of exchange on 2% DVB resin, we speculate that the interaction between the complex ion and water depends on the surface charge density of complex ion. Further, the heat of exchange on 2% DVB resin and the equivalent volume of resin are explained in terms of the interaction between the complex ion and water.