Column lysimeter studies were conducted to evaluate the long-term leaching characteristics of Ra-226 from coarse pyritic uranium mill tailings under unsaturated conditions. The influence of acid generation and release of other ionic species, and the role of sulphate ion control during leaching and post leaching periods on Ra-226 mobility were investigated. For a variety of leaching conditions, the solid-liquid partition coefficient, Kd, was also determined.
The tailings under unsaturated conditions oxidized rapidly and produced a strongly acidic drainage. Enhanced releases of Ra-226, Pb, U and Th were seen at the onset of the acidic drainage, of Ra-226 and Pb near the end of the leaching when the acid generation rate had decreased significantly, and of Ra-226 alone during the flushing of the tailings to remove oxidation reaction products.