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 = CoIII or CrIII, 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.