Confirmation of the retention of 226Ra in U-mine tailings by barite

2025

Article référencé dans le Web of Science WOS:001475464800001

Besançon C., Gérard Martine, Lahrouch F., Hughes K., Sardini P., Savoye S., Descostes M.

Journal of Hazardous Materials Advances, 2025, 18, p. 100716 [14 p.] ISSN 2772-4166

Uranium ore from the Athabasca basin in Saskatchewan Canada, particularly from the McClean Lake and Cigar Lake deposits, is extremely rich in uranium (U): 2 to 20-25 % U3O8. The ore is also rich in many elements considered to be Constituents of Potential Concern (COPC) for the environment, including arsenic (As), selenium (Se), nickel (Ni), molybdenum (Mo), lead (Pb), cobalt (Co) and radium-226 (226Ra). Following uranium extraction, residual materials (tailings) containing these elements in partially immobilized forms are placed in the McClean Lake plant Tailings Management Facility (TMF). Uranium tailings are sulfate-rich low-level radioactive waste containing 226Ra, with activities of up to 3000 Bq/g. Barium chloride (BaCl2) is added to precipitate 226Ra in barite as a solid-solution. Following this neutralisation treatment, 226Ra in the tailings is generally considered as sequestered in barite and sorbed onto ferrihydrite. To assess the subsequent stability of 226Ra in the tailings, an extensive study of its retention potential was performed. Characterisations incude assessment of tailings pore water and solids chemistry, tailings mineralogy, cation exchange capacity measurement, scanning electron microscopy and energy-dispersive x-ray spectroscopy (SEM/EDS), and alphaautoradiography analyses supplemented with thermodynamic modelling. This work confirms that barite is the main 226Ra binding-phase, in agreement with the 226Ra concentration measured in the porewater (6 Bq/L) resulting from a coprecipitation reaction. A (Ba,Ra)SO4 solid-solution regulates the average 226Ra concentration now and over the long term, through a distribution coefficient which is subject to a gradual shift towards a recrystallisation equilibrium. Recrystallisation causes an increase in the long-term concentration of 226Ra in the tailing water to 10 Bq/L. The work, conducted to assess the management strategy of the tailings, allowed us to ensure that the tailings have no significant effects on the downstream environment over the long term.

Sciences du milieu [021] ; Géologie et formations superficielles [064]

CANADA

Fonds IRD [F B010093454]

fdi:010093454