Migration of radium from the thorium ore deposit of Morro do Ferro,Poços de Caldas,Brazil

A large thorium ore deposit is located in Morro do Ferro, a hill in the Poços de Caldas Plateau, Minas Gerais, Brazil, which contains an estimated 30 000 t of Th and 100 t of U in a highly weathered matrix exposed to erosion and leaching. ²²⁸Ra and ²²⁶Ra were analyzed in surface waters collected at various points in the drainage basin and in groundwaters from wells drilled through and around the ore body. The concentrations in groundwater demonstrated that radium is markedly leached by rainwater percolating through the ore body. In its transit underground, radium is removed from groundwater by sorption on soil particles and this natural process greatly reduces the radium discharged to the environment. In dry weather, the concentration of dissolved ²²⁸Ra in the main stream draining the Morro do Ferro is 7·0 ± 1·1 mBq litre⁻¹ and in a control stream 1·6 ± 0·3 mBq litre⁻¹. The estimated ²²⁸Ra mobilization rate by solubilizations is of the order of 10⁻⁷ y⁻¹.     

Assessment of acid rock drainage pollutants release in the uranium mining site of Poços de Caldas--Brazil

We compared three different techniques to assess acid drainage occurrence connected to pyritic waste rock piles at a uranium mining and milling site in Po?os de Caldas--Brazil: (1) mass balance calculations, (2) column leaching experiments and (3) geochemical modelling. The study site was chosen because all the drainage coming from the pile is collected in one holding pond and a huge database (monitoring program) was available. The three independent methods predicted similar values for the intrinsic oxidation rate (IOR) (about 10(-9) kg m-3 s-1). We estimate the total time for consumption of all oxidizable material in the dump to be greater than 500 years. Geochemical model results showed a good agreement between predicted sulphate concentrations in relation to those found in the waste pile drainage, although the Al values were overestimated and pH values were underestimated.