The influence of a metal oxide surface on ligand exchange reactions between strong chelating agents

Agricultural, pulp and paper mill, and medical industries use synthetic aminocarboxylates called chelating agents to bind metal ions and control metal ion concentrations. These chelating agents often make their way into the environment where they can influence the distribution of metal species. One process that is affected is the exchange of the metal ion between chelating agents by a ligand exchange reaction. Our research examines how a surface, such as titanium dioxide (TiO₂), may affect the exchange of nickel between CDTA and EDTA, two common chelating agents. By examining the kinetics of these exchange reactions using capillary electrophoresis (CE) we hope to understand the role of surfaces in the exchange mechanism. As a first step to understanding the mechanism, we characterize the TiO₂ surface through various methods including measuring the number of reactive surface sites and the extents of adsorption of nickel, CDTA, EDTA, NiCDTA, and NiEDTA in TiO₂ suspensions at varying pH using CE and Atomic Absorption Spectroscopy.