Uranium and thorium leachability in contaminated stream sediments from a uranium minesite

The leachability and potential environmental risks of uranium (U) and thorium (Th) in aquifer sediments from a recent uranium minesite of northern Guangdong Province, China were investigated as part of ongoing environmental investigations. Data for the non-mineralogical portion of U, Th and of additional major elements (Mn, Fe, Ca, Mg, Na, Al and K) using a 0.5 mol/L HCl partial leach and inductively coupled plasma optical emission spectrometry (ICP-OES) were presented for the contaminated sediments and a background sediment. The contaminated sediments reported leachable contents of U between 22.85 and 2700 μg/g and those of Th between 4.800 and 102.1 μg/g, which exceed by a few to several hundred times the respective content found in the background. Generally, the leachable U and Th contents in the stream sediments decrease with distance from the potential contamination sources. A special case is the runoff gathering reservoir located around 1 km downstream of the U mine-site, representing the most severe metal contamination hotspot within the alpine watershed, where the highest leachable content of U and Th in the inlet sediment was observed. The highest leachability of U (68.6%) and Th (44.8%) was observed in this sediment as well, indicating a high potential of bioaccumulation and bioconcentration of U and Th under changing geochemical conditions. Correlations analysis indicates that the dilute HCl leachable fraction of U and Th bound in the sediments are strongly dependent on anthropogenic inputs from the U mining/milling activities, and Ca salts are the main vectors.