H2O2 and/or photocatalysis under UV-C irradiation for the removal of EDTA, a chelating agent present in nuclear waste waters

Abstract

In this study, we compare the efficiency of photocatalytic processes based on TiO2 (Degussa P-25) and UV/H2O2 as a means of degrading and mineralizing ethylenediaminetetraacetic acid (EDTA) under UV-C irradiation. EDTA was the molecule studied here because it is present in high proportions at nuclear facilities, where it is used for cleaning and decontamination purposes because of its chelating properties. The photonic power of the UV-C lamps used (13 and 15W) was established using actinometric and Keitz's methods. The adsorption of EDTA on TiO2 Degussa P-25 corresponds to a Langmuir isotherm, and the photocatalytic degradation process is consistent with the Langmuir–Hinshelwood model. During the photocatalytic process, an increase in the initial EDTA concentration favors the formation of large quantities of intermediates, which occupy the active sites, thus delaying the production of detectable quantities of oxalic acid. The results obtained here also show that nitrogen originating from EDTA molecules is mainly converted into ammonium and nitrate ions with a conversion rate of 67%. In addition, the amount of oxalic acid formed increases with the pH. The efficiency of the UV/TiO2 and UV/H2O2 processes as a means of EDTA degradation was found to be similar, provided H2O2 was added continuously during the UV/H2O2 process. The quantum efficiency was calculated and found to be equal to 0.9% in the case of photocatalysis and 1.4% in that of UV/H2O2.