Interaction of 54Mn and 55(59)Fe with EDTA in seawater and 0.55 M NaCl solutions

Interaction of ⁵⁴Mn and ⁵⁵⁽⁵⁹⁾Fe with EDTA in seawater and NaCl solutions was investigated by high-voltage paper electrophoresis. These two radionuclides were chosen because they represent two modes of behaviour of radionuclides in seawater—EDTA systems. In seawater without EDTA or at low EDTA concentrations in the systems ⁵⁴Mn behaves as a cation while ⁵⁵⁽⁵⁹⁾Fe gives a zone at the starting point of the electrophoretic strip. At higher EDTA concentrations, both radionuclides give only one anionic zone showing complexing with EDTA. In the intermediate range of the EDTA concentration (“transition region”) ⁵⁴Mn shows continuous change of the electrophoretic mobility from cationic to anionic (fast rate of interaction with EDTA), while ⁵⁵⁽⁵⁹⁾Fe reacts very slowly giving two well-separated zones in the transition region of the EDTA concentration.EDTA concentrations were varied from 10^?6 to 10^?2M, pH being adjusted to 8.0. The behaviour of radionuclides was followed by measuring the electrophoretic mobilities of radionuclides in dependence on the EDTA concentration at different aging times from 0 to 7 days.From the experimental data effective stability constants and the number of EDTA-ligands of ⁵⁴MnEDTA and ⁵⁵⁽⁵⁹⁾FeEDTA complexes in seawater and 0.55 M NaCl solutions were calculated.