A comparative waste management performance assessment of two uranium production units in Brazil

The Pocos de Caldas uranium production facility was closed in 1997, and a decommissioning programme started in 1998. The project was intended to produce 500 t U3O8/year and 275 t/year of calcium molybdate as a by-product. The key environmental aspect related to these entities deals with acid drainage. There is only one tailings dam at the site. It accumulates circa 2,05 x 106 tons of tailings, 85% being milled ore. The waste-rock/milled ore ratio is 60. Liquid effluents from the tailings dam are treated with lime and BaCl2. Acidification of the infiltrating waters is still of concern as a result of residual pyrite oxidation. It has been estimated that unrestricted use of the mill tailings area shall not be allowed because exposure to radon may imply in doses up to 40 mSv/year. The Caetite Unit started operation in 2000. The production has been raising, from 100 ton in 2001, up to 340 ton in 2003. It is expected that after 16 years of production 12,2 x 106 ton (6,8 x 106 m+3) of waste-rock material will be generated. This figure is approximately 10 times less than that reported for the Pocos de Caldas project. Differently from the Pocos de Caldas project, pyrite is not present in those rocks. Solid wastes from the industrial plant are composed by the leached ore piles. It is expected that 6 piles of 25.000 a 36.000 ton of ore are formed each year. The uranium liquor and washing waters present precipitated material composed by silica, sulfate, phosphate, titanium, iron and calcium besides uranium. These solids are separated from the uranium solution through filtration in activate coal filters. It can be seen that the uranium content in the leached ore represents 15% of the original ore and that the content of 226Ra is virtually the same. As result the leached ore piles may be a relevant source of 226Ra in the long term. It is expected that this scheme will reduce the fluxes of radionuclides from the piles to marginal levels without major environmental concerns After the solvent extraction uranium content in the liquor drops from 12 to 0,003 g/L. The most important aspect in the operation of the Caetite Unit is that liquid effluent emissions into the environment do not take place. One of the determining factors regarding the environmental performance of both units is the prevailing climatological condition at these sites. Rainfall rates of about 1,700 mm/year are observed at the Pocos de Caldas site. On the other hand this value drops to 800 mm/year at the Caetite site. Due to the highest rainfall rates observed at Pocos de Caldas site, an amount equivalent to US$ 3,35 million has been spent with acid drainage abatement (77% only with water treatment). Remediation plans for the Pocos de Caldas site include the, among other issues, stabilization of the uranium mill tailings dam, and abatement of acid mine drainage. In both cases it has been assessed that the application of dry covers will be the most adequate solution. Remediation costs associated with these measures are estimated to be in the range of US$ 3 to 10 million. In the case of Caetite unit ongoing closure of waste-rock piles and tailings ponds is taking place. Costs involved on these activities are not available. Although, it can be assumed that they will be much lower than those to be practiced at Pocos de Caldas site. The vulnerable aspect of the Caetite site has also to do with rainfall rates, but in an opposite direction. Since perennial water bodies are not available at the mine location, groundwater is of key relevance. Salinity of these waters poses significant difficulties for the uranium recovery operation. In addition, underground water bodies are very sensitive to pollution as they serve as water resource for local communities