Mining, Milling and Refining

Uranium ore is either dug out of the ground or the uranium is leached from the ore in the mine. Typically these mines are built to last in the order of 15 years. Drilling and blasting are used in either open pit (strip-mining) or underground mines. Because uranium is generally found in such low concentrations, huge amounts of rock must be mined. For every one tonne of uranium ore produced, there are 55 tonnes of tailings produced, when there is a concentration of 1.8 percent (1 tonne equals 1,000 kilograms). The uranium content of the ore is often between only 0.1 percent and 0.2 percent.

Before the uranium metal is extracted, the ore must be crushed into finer and finer fragments. After primary crushing, the ore is passed into a rotating ball mill, which grinds the rock into a fine powder. This powder is then treated to remove the uranium. The powder left over from the extraction of the uranium is called tailings. The minute size of these particles makes it impossible to keep them completely isolated from workers and the surrounding environment. In addition, the release of decay products of uranium into the biosphere is greatly accelerated.

While uranium deposits in Ontario generally have low concentrations of uranium, some of the ore bodies in Saskatchewan have more than 20 percent uranium. Lung cancer risks for miners in such ore bodies are so high that mining has been done by robots.

The ore is typically milled near the mine to reduce shipping costs. Huge amounts of water and chemicals are added to the pulverized ore. The uranium chemically bonds with a strong acid (sulfuric acid) or a strong base (caustic soda, also called sodium hydroxide) and, through a series of steps, about 90 percent of the uranium is separated from the host rock.

The last stage of drying, separating (centrifuging) and chemical precipitation, results in a product called yellowcake, which is a yellow to brown powder that contains 90 percent uranium oxide (U3O8). Once it is milled into yellowcake (U3O8), uranium in Canada is then sent to a refinery owned by Cameco Inc. at Blind River, Ontario, where it is further processed into uranium trioxide (UO3). The UO3 is then sent to Cameco’s Port Hope, Ontario facility, where it is processed into uranium hexafluoride (UF6) and uranium dioxide (UO2). The UF6 is treated to enrich the Uranium-235 to higher and higher concentrations. Uranium dioxide pellets are also made at a Zircatec plant at Port Hope for fuel rods for units of the Bruce nuclear power generating station. Uranium dioxide is also formed into pellets at the GE-Hitachi Nuclear Plant at 1025 Landsdowne Avenue in Toronto. These uranium dioxide pellets are then assembled into nuclear reactor fuel rods at Peterborough’s GE-Hitachi Nuclear Energy Canada Inc. facility.

Tailings Waste
Tailings are the left-over sludge after the uranium metal is extracted from the uranium ore. The half-lives of the principal radioactive components of mill tailings, Thorium-230 and Radium-226 are long, 75,000 and 1,600 years respectively. These tailings are pumped into tailings ponds and covered with water to reduce radioactive emissions and to prevent oxidation of sulfide-bearing rock. Some tailings are covered in clay for long-term storage. The clay sill keeps oxygen out of the tailings and reduces the amount of ground water moving through the radioactive area. In addition to the radioactive hazards, tailings may contain chemically hazardous substances including cyanide, arsenic, lead and mercury, which are able to get into the environment by seepage, leaching and blown dust.

Uranium in eastern Ontario is estimated to be between 0.1 percent and 0.2 percent. This means that for every kilogram of eastern Ontario uranium oxide produced, about one million (1,000,000) kilograms of ground up rock will be dumped into manmade lakes, also called tailing ponds.