Self-Purification Of Contaminated Solutions After Uranium In Situ Leaching

The sandstone type Devladivske uranium deposit is located within the limits of Eocene pale-ovalley filled with alluvial sediments. Mineralization with uranium content up to 0.1% forms several ore beds divided by redox barriers. In the period 1962-1983 the deposit has been exploited over an area of 918000m2 by in situ leaching (ISL) using drillholes with a depth between 35 and 100m. During mining operation about 200,000 t of H2SO4, 6,300 t of HNO3, and 15,000 t of NH4NO3, have been pumped in the ore body. In 1983, the groundwater pollution aureole had a length of 4.5 km and a width of 400-600 m. There is a hydraulic connection between the uranium-bearing aquifer and both the upper and lower ones. The technological solutions used for ISL caused partial contamination of these horizons. After mining completion, dilution of the residual technological solutions with "pure" natural waters took place through gaps in impermeable sediments between aquifer horizons. Calculation of self-purification process kinetics shows that the sulfate ion pollution aureole will disappear approximately after 120-150 years at a distance up to 2.0-2.5 km from the western margin of the deposit. This means that there is no risk for contamination of the river Saksagan? that flows at a distance of 17km from the deposit.