Degradation of a cobalt(II)-EDTA complex by photocatalysis and H2O2/UV-C. Application to nuclear wastes containing 60Co

The 60Co present in some low-level effluents forms complexes with organic ligands such as ethylenediaminetetraacetic acid (EDTA). These complexes make it difficult to remove the 60Co using conventional filtration methods. The aim of this study was to test the use of titanium-based photocatalysis (TiO2/UV) and photochemical methods involving the use of oxidation agents (H2O2/UV-C) (both of which are advanced oxidation processes) to degrade EDTA and recover 60Co once it has been released from the complex. In preliminary experiments on the 59Co-EDTA complex, we tested the efficiency of the TiO2/UV and H2O2/UV-C processes as means of degrading EDTA molecules and releasing cobalt in its cationic forms Co2+ and Co3+. These cations can be trapped by either precipitating and/or adsorbing them on TiO2 depending on the pH. When this treatment was applied experimentally to radioactive wastes, it turned out to be highly effective since it improved the decontamination factor (DF: initial volumic activity/final volumic activity) twofold. (author)