Chemical speciation of ethylenediamine-N,N′- disuccinic acid (EDDS) and its metal complexes in solution

Abstract

Computer simulation of chemical speciation has been used to assess the ability of the readily-biodegradable ligand SS-EDDS4− to replace the non readily-biodegradable ligand EDTA4−. Potential replacement ligands for EDTA4−, from the EDDS4− homologous series, which are readily biodegradable were assessed for their technical compatibility with EDTA4− using chemical speciation analysis based upon computer modelling. Chelating agents considered were EDTA(ethylenediaminetetraacetic acid), EDDS (ethylenediamine-N,N’-disuccinic acid), EDDM (ethylenediamaine-N,N’-dimalonic acid), and EDDG (ethylenediamine-N,N’-diglutaric acid) all producing 4-anionic ligands upon deprotonation. Formation constants with Ba2+, Sr2+, Mg2+, Ca2+, Mn2+, Cd2+, Co2+, Zn2+, Pb2+, Ni2+ , Cu2+, Hg2+ and Fe3+ions are listed (Table 2), some being determined as part of this study. The speciation modelling suggests that varying the total concentration conditions and using a limited supply of the EDDS ligand can, relative to EDTA, increase the complexing of Cu2+ in the presence of other ions, by a factor of 13, giving rise to the ‘more for less’ concept.