The importance of ligand speciation in environmental research: a case study

The speciations of EDTA and DTPA in process, waste and river waters are mod elled and simulated, specifically to the mode of occurrence in the pulp and paper mill effluents and subsequently in receiving waters. Due to relative ly short residence times in bleaching process and waste water treatment and slow exchange kinetics, it is expected that the thermodynamic equilibrium is not necessarily reached. Therefore, the initial speciation plays a key r ole. As such, the simulations have been extended to the process waters of t he pulp and paper industry taking into account estimated average conditions . The results reveal that the main species are; Mn and Ca complexes of EDTA and DTPA in pulp mill process waters; Fe(III) and Mn complexes of EDTA and DTPA in waste waters; Fe(III) and Zn complexes of EDTA and DTPA in receivi ng waters. It is also shown how the increasing concentration of complexing agents effects the speciation. Alkaline earth metal chelation plays a signi ficant role in the speciation of EDTA and DTPA when there is a noticeable m olar excess of complexing agents compared with transition metals. (C) 2001 Elsevier Science B.V. All rights reserved.