Occurrence, behavior and distribution of high levels of uranium in shallow groundwater at Datong basin, northern China

• Published in: The Science of the total environment Vol. 472; pp. 809 - 817
• Main Authors: Wu, Ya, Wang, Yanxin, Xie, Xianjun
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 15-02-2014; Elsevier
• Subjects: Applied sciences; China; Datong basin; Earth sciences; Earth, ocean, space; Exact sciences and technology; Geochemistry; Geologic Sediments - chemistry; Groundwater; Groundwater - chemistry; Groundwaters; Mineralogy; Natural water pollution; Pollution; Radiation Monitoring; Silicates; Uranium; Uranium - analysis; Water geochemistry; Water Pollutants, Radioactive - analysis; Water treatment and pollution; Asia; China; China, People's Rep; Geochemistry; Uranium; Groundwater; Datong basin; Complexation; Redox state; Permian; Sedimentary rock; Carboniferous; Radioisotope; Shallow water; Heavy metal; Trace element; Actinide; Adsorption; Shallow level; Northern China; Geogenic factor; Water pollution; Carbonates; Behavior; Ground water
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2013.11.109

Geochemical investigations of uranium (U) occurrence in the environments were conducted at Datong basin of northern China. The results suggest that U contents were generally <1mg/kg for the igneous and metamorphic rocks, typically 2–5mg/kg for the Carboniferous and Permian sedimentary rocks and around 3mg/kg for sediments and topsoil, respectively. U in the Quaternary aquifer sediments may be primarily associated with carnotite from the Carboniferous and Permian coal-bearing clastic rocks around the basin. Shallow groundwater had U concentrations of <0.02–288μg/L (average 24μg/L), with 24% of the investigated boreholes above the WHO provisional guideline of 30μg/L for U in drinking water. Average U concentration for surface water was 5.8μg/L. In oxidizing waters, uranyl (UO22+) species is dominant and strongly adsorbed onto iron (hydro)xides, while it would be preferentially complexed with carbonate in the alkaline groundwater, forming highly soluble uranyl-carbonate complexes at Datong. Under reducing conditions, uranous (U(IV)) species is ready to precipitate or bind to organic matter, therefore having a low mobility. At the study area, high U groundwater (>30μg/L) occurs at the alluvial plains due to intermediate redox and enhanced alkaline conditions. The abnormally high levels of U in groundwater (>100μg/L) are locally found at the west alluvial plains. By contrast, U co-precipitation with secondary carbonate minerals like Ca2UO2(CO3)3 in the dominant Ca–Mg–Na–HCO3 type groundwater may prevail at the east alluvial plains. Besides, bedrocks such as Carboniferous and Permian sedimentary rocks, especially the coal-bearing strata which have higher U contents at the west mountain areas may also account for the abnormally high levels of U in groundwater.
•High U groundwater occurs at the alluvial plains of Datong basin.•Redox state, complexation and adsorption are responsible for U enrichment.•Carboniferous and Permian sedimentary rocks have higher U contents at Datong.•Uranyl is preferentially complexed with carbonate in groundwater.•U in the aquifer sediments may be primarily associated with carnotite.