| Popis: |
Borewater monitoring near the Ranger U mine tailings dam has revealed deterioration in water quality in several bores since 1981, with increases in sulphate concentrations of up to 1000 times being observed. In some cases, significant increases in 226 Ra concentrations also occurred. In this study, isotopes of Ra, Th and Ac were measured in borewater in 1988–1993. For the most seepage-affected bores, the concentrations of 223 Ra, 224 Ra and 228 Ra as well as the nuclidic ratios 228 Ra/ 226 Ra, 223 Ra/ 226 Ra and 224 Ra/ 228 Ra generally increased. Time-series concentration increases were observed for Sr but not for Ba. 227 Ac concentrations increased with time, but not sufficiently to account for the increasing 223 Ra concentrations. It is concluded that increases observed in Ra isotope concentrations arise from competition for cation adsorption sites in the vicinity of the bore rather than by direct transport of Ra from the tailings. Formation of a barite solid phase is occurring in the groundwater and causing the removal of some Ra from solution, with rapid replenishment of the shorter-lived isotopes from their parents. |
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