MINERALOGICAL CHARACTERIZATION OF URANIUM ORE BLENDS AND RESULTING LEACH RESIDUES FROM KEY LAKE

An understanding of the solid reservoirs for potential metal and metalloid contaminants in uranium ore blends and leach resides is needed to predict their long-term controls in tailings porewaters. For this reason, the minerals hosting As, Mo, Ni, and Se in uranium ores and waste rocks used to blend with the ore in the milling process, and leach residues from the Key Lake mining operation, Saskatchewan were determined. Using x-ray diffraction, electron probe micro-analyzer and mineral liberation analyzer analyses, we determined that the reservoirs for As, Mo, Ni, and Se (in ores and blends) were dominated by sulphides including cobaltite, gersdorffite, molybdenite, pyrite, galena and chalcopyrite, secondary Ni-arsenates (annabergite and scorodite) and Ni-Co/Ni-sulfates. Secondary Ni-arsenates (annabergite and scorodite) and Ni-Co/Ni-sulfates in special wastes were major As, Mo, Ni, and Se bearing minerals, and are most likely the product of oxidation of arsenide minerals in special waste rocks. Analyses also showed that sulphides and arsenates occurred in trace amounts in the ores and special waste rocks (0.5 to 1.0 wt %). Our data showed that 55 to 90% pyrite, 36 to 51% chalcopyrite, 23 to 37% molybdenite, and 52 to 70% galena remained unleached in the resulting leach residues after milling of the ore blends. The percentages of unleached minerals varied between mill feeds, and were dependent on the grain-size distribution and the degree of mineral liberation.