Thermodynamic Model of Uranium and Arsenic Accumulation in Saline Lakes

Abstract

The attractiveness of Shaazgai-Nuur Soda Lake (pH 9.2 9.4) as an alternative metal source is explained by the high concentration of dissolved uranium (~1 mg/l) due to the location of water drainage territory within the TsaganShibetinskaya uranium-ore zone [Isupov et al., hereinafter]. Alkaline soda waters favor accumulation of uranium as uranyl-carbonate species, but uranium is accumulated in the Shaazgai-Nuur bottom sediments too. The total U concentration in bottom sediments is up to 10.4×10-2 g per kg of sediment, which is higher than the bulk concentration in water by two orders of magnitude. According to sequential extraction procedure, the most significant uranium solid species are ion-exchangeable and sorbed by iron (hydr)oxides. Besides uranium, the lake water contains rather high concentrations of B, Li and Sr. Noteworthy is the concentration of As as high as 250 μg/l. The concentration of uranium correlates positively with HCO3, As, B and Si. The purpose of this work was to simulate by means of thermodynamic calculations the main uranium and arsenic species in solutions and bottom sediments of Shaazgay-Nuur lake, and to offer a possible way of As removal as an undesirable impurity in commercial products.