Modelling of the dissolution and reprecipitation of uranium under oxidising conditions in the zone of shallow groundwater circulation

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 CO pressure (P, open system) of 10 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. Accumulation slows at the onset of saturation and precipitation of secondary uranium minerals at M = c. 1000 mg L (which, under baseline modelling conditions, also corresponds approximately to calcite saturation and transition to Na-HCO hydrofacies). The secondary minerals are typically "black" uranium oxides of mixed oxidation state (e.g. UO and UO). 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, but with typical concentrations of up to 10 μg L 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 P (low P favours higher pH, rapid accumulation of aqueous U and earlier saturation with respect to uranium minerals).

Multi‐Isotope Based Identification and Quantification of Oxygen Consuming Processes in Uranium Hosting Aquifers With CO2 + O2 In Situ Leaching

“…Groundwater physicochemical parameters critically control the U mobilization in aquifer systems containing U deposits, including pH, Eh, temperature, dissolved inorganic carbon, and reductants (Asghar et al., 2020; Blake et al., 2015; van Berk & Fu, 2017; Su et al., 2020). The U mobilization is closely linked to redox conditions, and the introduction of O 2 or NO 3 − into reduced aquatic systems leads to the dissolution of U‐bearing materials (Dutova et al., 2017; Pan et al., 2018; van Berk & Fu, 2017). pH controls dissolution, adsorption, complexation, colloid formation, and species of U (Mühr‐Ebert et al., 2019), which regulates U ore‐water interactions in aquifer systems (Asghar et al., 2020; Su et al., 2020).…”

The HydroGeo Software Package and Its Usage

“…3. Regional generalizations for hydrogeochemistry and petroleum hydrogeology of the Siberian Platform, the Western Siberian Plate and for geochemistry of groundwater of the Altai-Sayan folded area have been conducted [16][17][18].…”

Mineralogical characteristics of Uskol Lake sediments (Republic of Khakassia)

“…Букаты [Букаты, 2002]. Использование программного обеспечения HydroGeo для решения широкого спектра различных задач было продемонстрировано ранее [Дутова и др., 2006;Гаськова и др., 2009;Dutova et al, 2017. Наиболее внимательно и детально была изучена минералообразующая способность пресных подземных вод и соответствующие им минеральные новообразования [Вологдина и др., 2015; Покровский и др., 2002;.…”