Acid rock drainage and radiological environmental impacts. A study case of the Uranium mining and milling facilities at Poços de Caldas

Acid rock drainage generated as a result of sulphitic minerals oxidation is a source of pollution in many mining sites all around the world. This is the case at the Uranium Mining Site of Poços de Caldas, Brazil. The present study was aimed at studying the geochemical mechanisms involved on the mobilization of radionuclides from the waste rocks that occurs along with the acid drainage. The environmental radiological impacts caused by these pollutants were also assessed. It has been shown that precipitation of Ra and Pb as sulfates was the most important mechanism in the reduction of both radionuclides activity concentration in the acid drainage. A result of this study was that uranium isotopes were the most important radionuclides in terms of the exposure of the critical group. It has been suggested that the recovery of uranium from the acid drainage would be a feasible practice, economical aspects taken into account. It has also been estimated that pyrite oxidation will occur for more than a thousand years. The long time scale involved on the oxidation of the pyritic material implies the need for the adoption of permanent remedial actions. To assess applicable remediation strategies it has been suggested that oxygen and temperature profile determinations should be carried out in the dump.