Kinetic Study of Metal-EDTA Complex Formation and Metal-to-Metal Exchange between Free Metal Ions and Metal-EDTA Complex

In this study, the kinetics of metal-EDTA complex formation and metal-to-metal exchange between free metal ions and metal ions in metal-EDTA complex was investigated. The reactions of metals, Ca, Co, Cu, Fe (III), Mg, Mn, Ni, Al and Zn, with EDTA were carried out to understand how fast metal-EDTA complexes are formed at different pH and concentrations. The exchange kinetics between a free metal ion (Mn 2+ , Co 2+ , or Zn 2+ ) and a metal ion in its metal-EDTA complex were investigated. EDTA complexes with the free metal ions, were found to be formed almost instantaneously. The exchange between a free metal ion and a metal ion in its metal-EDTA complexes was generally fast (<30 min) when it occurred and seemed to be affected by pH but not by concentration. In general, a metal ion in its metal-EDTA complex could be replaced by a free metal ion, which forms a much more stable complex with EDTA than the former complex. Equilibrium constants for each reaction were calculated and compared with literature values. The results of this study would be useful to design physical/chemical/biological processes for removing metal-EDTA complexes.