Trace Metals Removal with Precipitated Solids from Uranium Mine Effluent at Cameco's Key Lake Operation

摘要

The removal of selenium and molybdenum from uranium mine effluent is complicated by the numerous redox states of molybdenum (Mo) and selenium (Se) as well as the increased solubility of precipitated Se and Mo in mine tailings above neutral pH. While co-precipitation with iron and the use of ferric sulfate-gypsum are accepted industrial practice for the removal of Mo and Se respectively, the molybdenum can be liberated from the Fe_2(MoO_4)_3 complex at pH levels greater than 6 and Se, if not in reduced forms, will remain mobilized in process solution. At the Cameco Key Lake uranium mine, innovations and extensive efforts have been applied to remove Se and Mo in the mill effluent stream to meet the regulatory permits. Additional pilot test work indicated Se and Mo levels could be reduced below permitted levels at a pH of 3.8 by using the proprietary FLSmidth MaxR? solids recycle process. At the same time, solids concentrations in the thickener underflow can reach 35-40 weight percentages which exhibit better solid/liquid separation characteristics and a decrease in the volume of waste for tailings disposal. Long term stability of the precipitated solids at neutral pH could also be achieved due to the encapsulation of the Se and Mo containing particles with gypsum using the MaxR? solids recycle process.