Complexation Study of Uranyl Ion with Dissolved Organic Matter in Natural Freshwater by Fluorescence Quenching Techniques

Abstract

The environmental problem of uranium waste has attracted global attention, and the investigation of its migration behavior in the environment has become an important topic. Uranyl ion is the most distributed form of uranium in water, and its mobility is highly affected by dissolved organic matter (DOM) due to its complexation in aquatic systems. In this study, DOMs in a variety of water samples from the Merrimack Valley of Massachusetts in the USA were studied using fluorescence excitation-emission matrix (EEM) techniques and regional integration analysis (RIA) data treatment method. RIA divided an EEM of DOM into five regions according to its fluorescence features and categorized them as humic-acid-like, fulvic-acid-like and amino-acid-like. Fluorescence quenching techniques were used to study the complexation properties of DOM with uranyl ion in aquatic systems at pH 3.5. Intense peaks in regions III and V were found to be quenched during the titration by uranyl ion. Results obtained showed that the stability constants (log K) were 4.01–4.19 and 3.83–3.97 for regions III and V, respectively. This study provides an easy, nondestructible and effective approach for studying the complexation of uranyl ion with DOM by applying the RIA method with fluorescence quenching. DOM and low C L values obtained, this method provided reliable results in measuring stability constants. From the results, two distinct peaks were observed in region III and region V and the fluorescence quenching of these two peaks was studied. The Concord River water showed the highest stability constants followed by Mascuppic Lake, Haggetts Pond, Merrimack River Lowell and Merrimack River Newburyport. Region V was less quench-able and lower in binding ability than region III. The fluorescence quenching method is easy and nondestructive to the sample and can be used to monitor natural water quality and conduct binding studies. Further study of a more complicated modeling such as mul-tisite binding modeling is needed to better understand the complexation of uranium with DOM in natural aquatic systems.