Precipitation of aluminum and magnesium secondary minerals from uranium mill raffinate (pH 1.0–10.5) and their controls on aqueous contaminants

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DOIResolve DOI: http://doi.org/10.1016/j.apgeochem.2015.09.002
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TypeArticle
Journal titleApplied Geochemistry
ISSN0883-2927
Volume64
Pages3042
Subjecttailings; uranium; aluminum; magnesium; arsenic; nickel
AbstractModels of geochemical controls on elements of concern (EOCs; e.g., As, Se, Mo, Ni) in U tailings are dominated by ferrihydrite. However, the evolution of aqueous concentrations of Al and Mg through the Key Lake (KL) U mill bulk neutralization process indicates that secondary Al and Mg minerals comprise a large portion of the tailings solids. X-ray diffraction, Al K-edge XAS, and TEM elemental mapping of solid samples collected from a pilot-scale continuous-flow synthetic raffinate neutralization system of the KL mill indicate the secondary Al–Mg minerals present include Mg–Al hydrotalcite, amorphous Al(OH)3, and an amorphous hydrobasaluminite-type phase. The ferrihydrite present contains Al and may be more accurately described as Al–Fe(OH)3. In the final combined tailings sample (pH 10.5) collected from the model experiments using raffinate with Al, Mg, and Fe, solid phase EOCs were associated with Al–Fe(OH)3 and Mg–Al hydrotalcite. In model experiments using raffinate devoid of Fe, aqueous EOC concentrations decreased greatly at pH 4.0 (i.e., where ferrihydrite would precipitate) and largely remained in the solid phase when increased to the terminal pH of 10.5; this suggests Al–Mg minerals can control aqueous concentrations of EOCs in the raffinate in the absence of Fe. Maximum adsorption capacities for individual and mixtures of adsorbates by Mg–Al hydrotalcite were determined. A revised model of the geochemical controls in U mill tailings is presented in which Al and Mg minerals co-exist with Fe minerals to control EOC concentrations.
Publication date
PublisherElsevier
LanguageEnglish
AffiliationNational Institute for Nanotechnology; National Research Council Canada
Peer reviewedYes
NPARC number23001585
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Record identifiera06e61a2-473a-44cd-af5a-f87a159a2648
Record created2017-03-08
Record modified2017-03-08
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