The exploitation of the Paal-Knorr reaction as a postmodification tool of ethene/propene/CO polyketone terpolymers to produce thermoset beads for metal ion uptake is hereby presented. Its prominent green character (i.e., no catalyst or a solvent employed, biocompatible polymer precursor) renders this class of functional polymers highly competitive in terms of low environmental impact compared to commercial biosorbents. Different cross-linking protocols are implemented for the four polymer resins, all involving formation of imine and/or pyrrolic bridges between the macromolecules. Functional thermosets bearing piperazine (X-PICPip), primary amine (X-PICDap) or glycine-type (X-PKLys) functional groups are synthesized. Qualitative correlation has been attempted with the metal ion-functional group interaction evaluation through FT-IR measurements and the correspondent uptake performances. During batch studies, the three resins indicated a robust uptake of Ni(II), Ag(I), and Cr(III), whereas in competitive adsorption during selectivity studies they showed a different reactivity pattern in the presence of the same metal ions.