Polymeric aminomethylphosphonic acids - 2. Polychelatogenes for separationof transition metal ions by membrane filtration

Investigations on the complex formation of monomeric and polymeric aminomet hylphosphonic acids with several transition metal ions were carried out. Th ese water-soluble complexes were separated from aqueous solution using an u ltrafiltration system. The maximal loading capacities of the polymeric chel atogenes with Cu2+, Cd2+, Hg2+, and Pb2+ ions were determined at various pH values. Mixed loading studies were carried out to determine the selectivit y of these macromolecular chelating agents for metal ions. Compared with kn own aminoalkylphosphonic acid groups containing polymers, the polyacryloyla minomethylphosphonic acid in particular exhibits good complexation ability for the transition metal ions Cd2+ and Hg2+. The acid-base equilibria and c omplexation behavior of these polychelatogenes were investigated. Acid diss ociation constants of the chelating agents and the formation constants of t he chelates were determined by means of potentiometric titration. Spectroph otometry was used to determine the dependence of the metal ion/ligand ratio of the formed complexes on the pH. The structure of the formed complexes w as investigated using IR spectroscopy. Proposals for the structures of the complexes were made on the basis of these measurements.