The Speciation of U(VI) Complexes in Solutions by TRLIF Spectroscopy

Speciation of actinide in natural aquatic system is of great interest for the safety assessment of a nuclear waste disposal in deep geological system. Actinide ions form complicate complexes with various ligands such as OH-, CO32-, and humic substances in groundwater. These complexes can enhance or reduce the migration of actinide elements. The direct speciation of these complexes in groundwater requires a highly sensitive and selective method which is capable to determine trace amount of actinides (down to 10-9 M) and to identify the different complexes without separation. Time-resolved laser-induced fluorescence (TRLIF) spectroscopy is a very suitable method for trace analysis of some actinides such as uranium, curium and americium due to their fluorescence feature. In our recent work, a TRLIF system using a photomultiplier tube (PMT) coupled to a spectrometer was applied to investigate various U(VI) complexes. In this work, a modified TRLIF system using an intensified charge-coupled device (ICCD) camera is introduced and its performance is compared with the previous system for the speciation of uranium complexes. We have investigated the effect of background materials, such as HClO4 and NaClO4, on the lifetime of the UO22+ ions in liquid solutions. In addition, the speciation of U(VI)-OH complexes has been carried out in considering the lifetime of the free uranyl ions at a certain background material