Decontamination of Elliot Lake uranium tailings

CIM Bulletin, Vol. 72, No. 808, 1979

D. RAICEVIC, Research Scientist, Ore Processing Laboratory, Mineral Sciences Laboratories, CANMET, Energy, Mines and Resources Canada, Ottawa

After more than 93% of the uranium is extracted from Elliot Lake uranium ores by a sulphuric acid leaching process, the leach residue (tailings) contains small amounts of uranium and radioactive isotopes, particularly radium-226, which is the most serious health hazard. Heavy metal components and pyrite are also present, along with the gangue minerals. Currently, over 1000 acres of the Elliot Lake area are covered with these tailings, which contain over five million tons of pyrite.Because of constant oxidation of the pyrite by bacteria (thiobacillus) and the presence of moisture, pyrite slowly generates sulphuric acid, which steadily leaches the metal-bearing constituents from the tailings. The seepage-flows of the dissolved contaminants, although often quite low in volume, have an environmental impact on the Elliot Lake area. Although these seepages are treated and most of the contaminants removed and impounded, a small amount of the radioactive contaminants reaches Lake Huron via the Serpent River.This paper describes a flotation approach for treatment of the Elliot Lake uranium tailings to produce new, deconlaminated tailings practically free of pyrite, with radium, thorium and uranium contents considerably reduced. The decontaminated tailing produced, which comprises about 75% by weight of the current uranium tailings, appears to be suitable for mine backfill. Because mine backfilling normally uses about 50% of the plant tailings, the surface storage of about half of the uranium tailings, therefore, would be eliminated by this process. Mine backfilling would also increase the mine production and thus enlarge the over-all uranium resources due to recovery of the ore from pillars. The pyrite concentrate produced from the current uranium tailings would be suitable for sulphuric acid production.The possibility of uranium recovery, and disposal of radium and thorium from the concentrates produced, is now being studied at CANMET.
Keywords: Uranium tailings, Elliot Lake, Decontamination, Radioactivity, Flotation, Pyrite, Tailings disposal, Environmental control.