Optical Properties of the Suwannee River Fulvic Acid Complexation with Thorium Using 3D Fluorescence Spectroscopy

The relationship between the complexation amount of thorium (Th) and Suwannee River fulvic acid (SRFA) and the changes in Th concentration and pH were studied using differential spectroscopy and 3D excitationemission matrix fluorescence spectroscopy (3D EEM). Experiments were performed at different Th concentrations and pH values. In the differential spectra at different concentrations, four bands of aromatic components appeared, and thorium was complexed with the carboxyl groups in SRFA. The 3D EEM spectra showed a fulvic acid-like fluorescence region, a visible-light fulvic acid region, and the blueshift phenomenon. The fluorescence intensity decreased with increasing thorium concentration and increased with increasing pH. The results showed that the amount of complexation of thorium and SRFA increased with increasing thorium concentration, and high pH was not conducive to the complexation of thorium and SRFA.