Bacterial Leaching in Uranium Mine Effluents at the Ore Treatment Unit, Caldas, Brazil

The condition for bacterial leaching (Acidithiobacillus spp.) in uranium ores is the presence of metallic sulphides such as associated pyrite (FeS₂), which occurs in the ore and waste rock piles of the Uranium Ore Treatment Unit (UTM), Minas Gerais State, Brazil. In the UTM area, water sampling was conducted at three points in the UTM interface environment, at two other points in the region (the open pit mine and waste rock piles) and at two points in the tailings dam. Chemical and bioleaching bacteria density analyses were performed using each sample. Water samples from all sampling points at the UTM interface, namely Points 25, 76 and 41, presented mean values of manganese concentration (0.10 mg/L) and fluoride (1.40 mg/L) which exceeded the limits established by Brazilian legislation. The mean value of uranium concentration found at Point 76 (0.13 mg/L) was also above the limit established by Brazilian legislation. Water samples from P76 (UTM interface) were considered susceptible to acid mine drainage and to the activity of bacteria involved in the bioleaching of metals. The chemical and microbiological results obtained in this study support the need to review actions currently employed by UTM for effluent control. (author)