Spectroscopic Study on the Ternary Complex Formation of U(VI) with Salicylic Acid

From the nuclear chemical point of view, ternary complex formation of actinide ions with ligands has attracted attention for understanding radionuclides' migration in the environment. There are various ligands in natural aquatic systems which can form stable ternary actinide complexes. Humic substance in a near-neutral groundwater is one of them and carboxylic groups in a humic substance are considered as the most likely functional group which interacts with actinides. In this work, the formation of the ternary complex of U(VI) with salicylic acid (SAH2) was investigated by two different laser-based spectroscopic methods, i.e., laser-induced breakdown detection (LIBD) and time-resolved laser fluorescence spectroscopy (TRLFS). The notable features are as follows: (i) the breakdown probability increases slightly, (ii) the absorbance of U(VI) increases, whereas the fluorescence intensity decreases with increasing salicylic acid concentration. The increase of the breakdown probability indicates that insoluble species are formed due to the complexation of U(VI) with SAH2. The decrease of the fluorescence intensity is due to the quenching effect of the SAH2 in the complexes. With regards to the instrumentation, the characteristics of a newly developed LIBD system adopting a probe beam deflection method are presented. We report also on the improved speciation sensitivity (∼10-9M for UO22+) of the TRLFS system