SORPTION OF PROTON AND HEAVY-METAL IONS ON A MACROPOROUS CHELATING RESIN WITH AN IMINODIACETATE ACTIVE GROUP AS A FUNCTION OF TEMPERATURE

A macroporous resin containing iminodiacetic groups (Lewatit) was inve stigated for its sorption properties towards proton and nickel(II) and cadmium(II). Different compositions of the aqueous phase, and differe nt temperatures were examined. The stoichiometry, the exchange coeffic ients and the intrinsic constants of the sorption equilibria were obta ined from the experimental data by using the Gibbs-Donnan model for th e ion exchange resin. The intrinsic constants were found to be indepen dent of the composition of the solution, so that they were used for ch aracterizing the sorption equilibria. While the first intrinsic proton ation constant of the active groups in the resin was found to depend o n the temperature, the second one was independent. The sorption equili brium of nickel in the resin was different from that of cadmium, being ascribable respectively to the formation of the complexes NiL and Cd( HL)(2). inside the resin. Their intrinsic complexation constants were found to be 10(-1.84) and 10(-3.64) at 25 degrees C. Compared to those of another resin with the same active groups, but not macroporous, th ey are higher. The dependence of the intrinsic constant on the tempera ture was also different for the two metals, allowing to evaluate a Del ta H degrees of + 30.9 and of + 13.7 kJ mol(-1) respectively. When a c omparison is possible, these values are near to those in aqueous solut ion for the complexation with ligands of similar structure. These resu lts can be used to achieve metal ion separation based on temperature v ariations. (C) 1998 Elsevier Science B.V. All rights reserved.