Studies on biodegradable chelating ligands: complexation of iminodisuccinic acid (ISA) with Cu(ii), Zn(ii), Mn(ii) and Fe(iii) ions in aqueous solution

Abstract

In a search for biodegradable chelating ligands for industrial applications, study was made of the protonation and complex formation equilibria of iminodisuccinic acid (ISA) as a mixture of two of its stereoisomers (50% [S,S] and 50% [R,S]) with Cu(II), Zn(II), Mn(II) and Fe(III) ions in aqueous 0.1 M NaCl solution by potentiometric titration at 25 °C. The model of the complexation and the stability constants of the different complexes were determined for each metal ion using the computer program SUPERQUAD. With all metals the complex formation was dominated by stable MLn − 4 complexes. Biodegradable and of low nitrogen content, ISA was found to be a good chelating agent in pulp bleaching.