Dutova, E. M., Nikitenkov, A. N., Pokrovskiy, V. D., Banks, D., Frengstad, B. S., & Parnachev, V. P. (2017). Modelling of the dissolution and reprecipitation of uranium under oxidising conditions in the zone of shallow groundwater circulation. Journal of Environmental Radioactivity, 178-179, 63–76.
Abstract: Generic hydrochemical modelling of a grantoid-groundwater system, using the Russian software “HydroGeo”, has been carried out with an emphasis on simulating the accumulation of uranium in the aqueous phase. The baseline model run simulates shallow granitoid aquifers (U content 5 ppm) under conditions broadly representative of southern Norway and southwestern Siberia: i.e. temperature 10 °C, equilibrated with a soil gas partial CO2 pressure (PCO2, open system) of 10−2.5 atm. and a mildly oxidising redox environment (Eh = +50 mV). Modelling indicates that aqueous uranium accumulates in parallel with total dissolved solids (or groundwater mineralisation M – regarded as an indicator of degree of hydrochemical evolution), accumulating most rapidly when M = 550–1000 mg L−1. Accumulation slows at the onset of saturation and precipitation of secondary uranium minerals at M = c. 1000 mg L−1 (which, under baseline modelling conditions, also corresponds approximately to calcite saturation and transition to Na-HCO3 hydrofacies). The secondary minerals are typically “black” uranium oxides of mixed oxidation state (e.g. U3O7 and U4O9). For rock U content of 5–50 ppm, it is possible to generate a wide variety of aqueous uranium concentrations, up to a maximum of just over 1 mg L−1, but with typical concentrations of up to 10 μg L−1 for modest degrees of hydrochemical maturity (as indicated by M). These observations correspond extremely well with real groundwater analyses from the Altai-Sayan region of Russia and Norwegian crystalline bedrock aquifers. The timing (with respect to M) and degree of aqueous uranium accumulation are also sensitive to Eh (greater mobilisation at higher Eh), uranium content of rocks (aqueous concentration increases as rock content increases) and PCO2 (low PCO2 favours higher pH, rapid accumulation of aqueous U and earlier saturation with respect to uranium minerals).
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Alvarado, J. A. C., Balsiger, B., Röllin, S., Jakob, A., & Burger, M. (2014). Radioactive and chemical contamination of the water resources in the former uranium mining and milling sites of Mailuu Suu (Kyrgyzstan). Journal of Environmental Radioactivity, 138, 1–10.
Abstract: An assessment of the radioactive and chemical contamination of the water resources at the former uranium mines and processing sites of Mailuu-Suu, in Kyrgyzstan, was carried out. A large number of water samples were collected from the drinking water distribution system (DWDS), rivers, shallow aquifers and drainage water from the mine tailings. Radionuclides and trace metal contents in water from the DWDS were low in general, but were extremely high for Fe, Al and Mn. These elements were associated with the particle fractions in the water and strongly correlated with high turbidity levels. Overall, these results suggest that water from the DWDS does not represent a serious radiological hazard to the Mailuu Suu population. However, due to the high turbidities and contents of some elements, this water is not good quality drinking water. Water from artesian and dug wells were characterized by elevated levels of U (up to 10 μg/L) and some trace elements (e.g. As, Se, Cr, V and F) and anions (e.g. Cl−, NO3−, SO42−). In two artesian wells, the WHO guideline value of 10 μg/L for As in water was exceeded. As the artesian wells are used as a source of drinking water by a large number of households, special care should be taken in order to stay within the WHO recommended guidelines. Drainage water from the mine tailings was as expected highly contaminated with many chemicals (e.g. As) and radioactive contaminants (e.g. U). The concentrations of U were more than 200 times the WHO guideline value of 30 μg/L for U in drinking water. A large variation in 234U/238U isotopic ratios in water was observed, with values near equilibrium at the mine tailings and far from equilibrium outside this area (reaching ratios of 2.3 in the artesian well). This result highlights the potential use of this ratio as an indicator of the origin of U contamination in Mailuu Suu.
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