Application of sequential extraction for analyzing source and sink of uranium in Huanghe River sediments, China

Geochemical behaviors of heavy metals are closely related to their chemical state that can be divided by sequential extraction into exchangeable (F1), bound to carbonates (F2), bound to Fe-Mn oxides (F3), bound to organic matter or sulfide (F4), and residual (F5). Uranium in sediment of the Huanghe (Yellow) River, China, in different chemical states was extracted using the five-step procedure of Tessier and the source and sink were analyzed. Results show that more than 70% of the total uranium was immobile residual F5 in abundance, followed in order of F4>F3>F2>F1, indicating that the main source of uranium in the sediments was from weathered rock in the drainage basin. In addition, the uranium in the sediments presents potential exogenous input in the Lanzhou, Baotou, and Tongguan reach. Fe-Mn oxides are main carriers of unstable uranium, especially those of F1 and F3. Calcite and illite are secondary adsorption minerals of unstable uranium in sediments under natural conditions. Human activities can also produce an obvious impact on uranium speciation. This study provides a reference for the application of sequential extraction in analyzing the source and sink of uranium in river sediments.