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

Dutova, E. M., Nikitenkov, A. N., Pokrovskiy, V. D., Banks, D. , Frengstad, B. S. and 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, 178-17, pp. 63-76. (doi:10.1016/j.jenvrad.2017.07.016) (PMID:28780371)

[img]
Preview
Text
146083.pdf - Accepted Version
Available under License Creative Commons Attribution Non-commercial No Derivatives.

3MB

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).

Item Type:Articles
Keywords:Groundwater, hydrochemical modelling, mineralisation, natural uranium, ore, solubility
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Banks, Mr David
Authors: Dutova, E. M., Nikitenkov, A. N., Pokrovskiy, V. D., Banks, D., Frengstad, B. S., and Parnachev, V. P.
College/School:College of Science and Engineering > School of Engineering
Journal Name:Journal of Environmental Radioactivity
Publisher:Elsevier
ISSN:0265-931X
ISSN (Online):1879-1700
Published Online:04 August 2017
Copyright Holders:Copyright © 2017 Elsevier Ltd.
First Published:First published in Journal of Environmental Radioactivity 178-179:63-76
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher

University Staff: Request a correction | Enlighten Editors: Update this record