Management of uranium mill tailing: Geochemical processes and radiological risk assessment

Abstract

This paper describes the geochemical processes regulating the mobilisation of heavy metals and radionuclides in the tailing dam of the uranium mining and milling facilities of Poços de Caldas, Brazil. The operational effluent release pollution of surface and groundwater was evaluated by means of monitoring data. The potential environmental impact after the future closure of the installation was assessed by means of dose estimations assuming the absence of remedial measures. Residual tailing pyrite oxidation was found to be the critical factor in the transfer of metals and radionuclides to seepage water. No contamination of deep groundwater was observed. On the other hand, the surface water of a nearby river revealed greater uranium concentrations in the tailing dam effluent discharge area than in a background river location sampling station. Lead-210 and 210Po were the principal contributors to the total dose while vegetables were the chief pathways of exposure, both for adults and children, to the studied radionuclides after closure. The results of the dose assessment indicate that permanent remedial actions will have to be adopted in the decommissioning phase.