Colloid-facilitated transport of uranium by groundwater at the U–Mo ore field in eastern Transbaikalia

The main objective of the study is field-scale analysis of colloid-facilitated transport of uranium from an underground source to the biosphere as applied to safety assessment of underground repository of spent nuclear fuel (SNF). The uranium deposit (Antei) in eastern Transbaikalia is considered as a natural analog of an underground repository of SNF. Transport of colloid-borne uranium by groundwater from the ore zone to the earth surface is examined. Groundwater at the uranium deposit site was sampled both in the ore zone (at the depth of approximately 750 m) and from the subsurface water. Extraction of the uranium-bearing colloid from the water samples was carried out by subsequent filtration through membranes with decreasing pore size. Uranium concentrations in the filtrate were measured by the methods of light-emitting diode-induced luminescence and inductively coupled plasma mass spectrometry. Chemical composition of the surface of the uranium-bearing colloid particles was determined by the methods of X-ray photoelectron spectroscopy with ionic etching and transmission electron microscopy. It is revealed that uranium-bearing colloid in the ore zone and at the earth surface consists of particles of different types (intrinsic colloid and pseudocolloid).