Characterizing and quantifying controls on arsenic solubility over a pH range of 1-11 in a uranium mill-scale experiment

Moldovan, B. J. and Hendry, M. J. (2005) Characterizing and quantifying controls on arsenic solubility over a pH range of 1-11 in a uranium mill-scale experiment. Environmental Science and Technology, 39(13), pp. 4913-4920. (doi: 10.1021/es0482785)

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A mill-scale hydrometallurgical experiment (2700 m3 of effluent treated/day) was conducted for three months at the Rabbit Lake uranium mine site located in northern Saskatchewan, Canada, to determine the controls on the solubility of dissolved arsenic over a pH range of 1−11 and to develop a thermodynamic database for the dominant mineralogical controls on arsenic in the mill and the resulting mill tailings. The arsenic concentrations in the mill ranged from 526 mg/L at pH 1.0 (initial) to 1.34 mg/L at pH 10.8 (final discharge). Geochemical modeling of the chemistry data shows that arsenic solubility is controlled by the formation of scorodite (FeAsO4·2H2O) from pH 2.4 to pH 3.1, with 99.8% of dissolved arsenic precipitated as scorodite. Model results show that scorodite is unstable (releasing arsenic back in to solution) above pH 3.1 and arsenic adsorption to the surface of 2-line ferrihydrite is the dominant controlling factor in the solubility of arsenic from pH 3.2 to pH 11.0, with 99.8% of dissolved arsenic removed from solution via this mechanism. Finally, model results show ∼0.2% of the total dissolved arsenic adsorbs to the surface of amorphous aluminum hydroxide from pH 5.0 to pH 8.0. Minor alterations to the thermodynamic properties of arsenite and arsenate adsorption to 2-line ferrihydrite allowed the fit between measured mill-scale and modeled concentrations for the pH range of 3.2−11.0 to be optimized.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Hendry, Professor Martin
Authors: Moldovan, B. J., and Hendry, M. J.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Environmental Science and Technology
Journal Abbr.:EST
Publisher:American Chemical Society
ISSN (Online):1520-5851

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