RATE CONTROLLING PROCESSES IN THE RELEASE OF RA-226 FROM URANIUM MILL TAILINGS .1. LEACHING STUDY

Uranium mill tailings (a pyritic quartz conglomerate ore) obtained from a Canadian operation were leached according to a modification of the method recommended by I.A.E.A. for the leaching of radioactive ions from solidified wastes. A static leach test procedure was chosen to provide information to permit an assessment of hazard due to release of Ra-226 to the environment. Narrow range size fractions (53 to 75 μm) of both fresh material obtained directly from a tailings line and material weathered for approximately 10 to 15 yr in a tailings basin were leached for up to 70 days. Distilled water and an acidic synthetic effluent (pH 2.5) were chosen as leachants. Two sequential desorption processes were observed, one before and the other after a leaching period of approximately 10 to 15 days. In the later and more significant stage of desorption, the leaching behaviour could be described in terms of a diffusion mechanism. Significantly greater quantities of 226Ra were leached over relatively short leaching periods by the acidic effluent; thus the quality of the effluent and percolating water in a tailings disposal area would markedly affect the leachability of Ra from tailings. It was also found that the quantities of 226Ra leached were significantly influenced by the solid: liquid ratio at low leaching volumes. © 1979 D. Reidel Publishing Co.