Evaluation of in vitro dissolution rates of thorium in uranium mill tailings.

Dissolution rates of thorium from the uranium mill tailings piles at two Department of Energy Uranium Mill Tailings Remedial Action Project (UMTRAP) sites have been evaluated. The thorium dissolution rates were evaluated in vitro using simulated lung fluid. The former uranium mills at the UMTRAP sites employed different chemical processes (acid leach and alkaline pressure leach) to extract the uranium from the ore, and the thorium dissolution rates at these sites were found to be markedly different. A site specific annual limit on intake (ALI) value for 230Th was calculated for the UMTRAP site that was associated with a multiple component dissolution curve.