Sorption of proton and heavy metal ions on a macroporous chelating resin with a iminodiacetate active group as a function of temperature

A macroporous resin containing iminodiacetic groups (Lewatit) was investigated for its sorption properties towards proton and nickel(II) and cadmium(II). Different compositions of the aqueous phase, and different temperatures were examined. The stoichiometry, the exchange coefficients and the intrinsic constants of the sorption equilibria were obtained from the experimental data by using the Gibbs–Donnan model for the ion exchange resin. The intrinsic constants were found to be independent of the composition of the solution, so that they were used for characterizing the sorption equilibria. While the first intrinsic protonation constant of the active groups in the resin was found to depend on the temperature, the second one was independent. The sorption equilibrium 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°C. Compared to those of another resin with the same active groups, but not macroporous, they are higher. The dependence of the intrinsic constant on the temperature was also different for the two metals, allowing to evaluate a DH° of 30.9 and of 13.7 kJ mol-1 respectively. When a comparison is possible, these values are near to those in aqueous solution for the complexation with ligands of similar structure. These results can be used to achieve metal ion separation based on temperature variations.