Acid rock drainage and radiological environmental impacts. A study case ofthe Uranium mining and milling facilities at Pocos 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 t he case at the Uranium Mining Site of Pocos de Caldas, Brazil. The present study was aimed at studying the geochemical mechanisms involved on the mobi lization of radionuclides from the waste rocks that occurs along with the a cid drainage. The environmental radiological impacts caused by these pollut ants 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 radio nuclides activity concentration in the acid drainage. A result of this stud y was that uranium isotopes were the most important radionuclides in terms of the exposure of the critical group. It has been suggested that the recov ery of uranium from the acid drainage would be a feasible practice, economi cal aspects taken into account. It has also been estimated that pyrite oxid ation will occur for more than a thousand years. The long time scale involv ed on the oxidation of the pyritic material implies the need for the adopti on of permanent remedial actions. To assess applicable remediation strategi es it has been suggested that oxygen and temperature profile determinations should be carried out in the dump. (C) 1998 Elsevier Science Ltd. All righ ts reserved.