Evaluation of availability and mobility of metals in contaminated sediments from an industry reservoir mining

Acid mine drainage (AMD) generates acid waters containing a wide variety of toxic metals and sulfur species, mainly sulfate, which can contaminate groundwater, lakes and rivers. Sulfate reducing bacteria in anaerobic environment can reduce this sulfate to sulfide, which can react with divalent metals to form insoluble species, decreasing the chemical activity and thus the bioavailability of these contaminants. The present study investigated sediments of the Aguas Claras reservoir which was affected by metals and radionuclides from the AMD process of a former uranium mine in Caldas, Minas Gerais State. Twelve surface water and sediment samples were collected with two background points located upstream of the reservoir. Measurements of acid volatile sulfide (AVS) were carried out to verify the extent of sulfate bacterial reduction. The analyses of sequential extraction were performed to establish the potential mobility and bioavailability of the contaminants. The AVS ranged from 2.3 to 5.7 mgS^2-g^-1 with background results of 0.01 and 0.4 mgS^2-g^-1. These results indicate that sulfate is being reduced to sulfide. The results of the sequential extraction indicated that U, Zn and Mn are associated mainly with the labile and reducible fractions. (author)