Conditions affecting the release of thorium and uranium from the tailings of a niobium mine. (April 2019)

• Record Type: Journal Article
• Authors: Li, Zhizhong; Hadioui, Madjid; Wilkinson, Kevin J.
• Is Part Of: Environmental pollution. Volume 247(2019)
• Page Start: 206
• Page End: 215
• Publication Date: 2019-04
• Subjects: Mobility -- Thorium -- Uranium -- pH -- Ions -- Fulvic acid; Pollution -- Periodicals; Pollution -- Environmental aspects -- Periodicals; Environmental Pollution -- Periodicals; Pollution -- Périodiques; Pollution -- Aspect de l'environnement -- Périodiques; Pollution -- Effets physiologiques -- Périodiques; Pollution; Pollution -- Environmental aspects; Periodicals; Electronic journals; 363.73
• DOI: 10.1016/j.envpol.2018.12.042
• Languages: English
• ISSNs: 0269-7491

Abstract

Abstract: Determinations of the mobility of metals from tailings is a critical part of any assessment of the environmental impacts of mining activities. The leaching of thorium and uranium from the tailings of different processing stages of a niobium mine was investigated for several pH, ionic strengths and concentrations of natural organic matter (NOM). The pH of the leaching solution did not have a noticeable impact on the extraction of Th, however, for pH values below 4, increased U mobilization was observed. Similarly, only a small fraction of Th (0.05%, ≤15 μg kg −1 ) and U (1.22%, ≤6 μg kg −1 ) were mobilized from the tailings in the presence of environmentally relevant concentrations of Ca, Mg or Na. However, in the presence of 10 mg L −1 of fulvic acid, much higher concentrations of ca. 700 μg kg −1 of Th and 35 μg kg −1 of U could be extracted from the tailings. Generally, colloidal forms of Th and dissolved forms of U were mobilized from the tailings, however, in the presence of the fulvic acid, both dissolved and colloidal forms of the two actinides were observed. Single Particle ICP-MS was used to confirm the presence of Th (and U) containing colloids where significant numbers (up to 10 7 mL −1 ) of Th and U containing colloids were found, even in 0.2 μm filtered extracts. Although mass equivalent diameters in the range of 6–13 nm Th and 6–9 nm for U could be estimated (based upon the presence of an oxyhydroxide), most of the colloidal mass was attributed to larger (>200 nm) heterocomposite particles. Graphical abstract: Image 1 Highlights: For variable pH and hardness, only small amounts of colloidal Th and ionic U were released from niobium tailings. In the presence of organic matter, much higher concentrations of both colloidal and ionic Th and U were released. Single particle ICPMS indicated mobilization of small colloids containing both Th and U.