Preparation of water-soluble chelating aminated starch derivatives and their use for the concentration of metal ions by ultrafiltration

Abstract

Water-soluble chelating starch derivatives bearing aminated ligands (diethanolamine, St-DEA; ethylenediamine, St-EDA; tetraethylenepentamine, St-TEPA) were prepared. Stoichiometries and stability constants of Cu 11-St-EDA complexes were determined by the Fronaeus method. The concentration by ultrafiltration of Cu 2+ ion solutions in the presence of aminated starches was investigated as a function of the molar ratio ligand: metal (retention coefficient, R, 95–99%). Higher retention coefficients were expected when considering the high stability constants of the complexing EDA and TEPA ligands. The amine assays of the filtrates show that the membrane lets small amounts of the polymer pass. This is due to distribution of the pore-size within the mmebrane, as confirmed by the R values for standard dextrans of various membranes. In the case of strong-complexing polymers such as St-EDA and St-TEPA, the measured metal transfer corresponds actually to the metal bound to the macromolecular ligand. These results are discussed in terms of membrane molecular weight cut-off, the relation between metal transfer and stability constants of complexion, and efficiency of metal ion concentration by ultrafiltration.