High-grade ore slurry arriving at the Key Lake ore slurry receiving plant is unloaded from the truck mounted containers by a vacuum aspiration system and pumped to one of four large air agitated slurry storage pachucas.

McArthur River low-grade mineralization and legacy low-grade mineralized waste stored at Key Lake on the low-grade mineralization blend pads is delivered to the grinding circuit grizzly by loader. The grinding circuit consists of a SAG mill in open circuit with a sizing screen. The screen oversize reports to the ball mill in closed circuit with two sizing screens. The undersize from all three screens report to the neutral thickener. The neutral thickener overflow is combined with industrial water to be re-used throughout the circuit.

High-grade ore slurry is withdrawn from the ore storage pachucas and pumped to the blending tank where it is mixed with the neutral thickener underflow. The resulting slurry is pumped to one of three storage pachucas located in the leaching plant. Blending is necessary as the original Key Lake processing facilities were not designed from a radiation protection perspective to accommodate the high ore grades found at McArthur River. In addition to reducing the radiation exposure in the mill, the dilution of the high-grade ore serves two other purposes: recovery of uranium from the low-grade mineralized material; and final disposal of the low-grade mineralized waste.

The uranium is leached from the ore in the atmospheric leach pachuca and three continuous stirred tank reactors, while uranium-bearing solution is separated from waste solids in the counter current decantation (CCD) wash circuit. The high pressure autoclave secondary leaching circuit is on stand-by as the current ore is amenable to leaching at atmospheric pressure. Sulphuric acid, steam and oxygen are injected into the leach vessels to promote uranium extraction.

The CCD circuit consists of eight thickeners in series. The slurry flow is counter current to the wash water. The slurry moves from thickener one to thickener eight, while the wash water moves from thickener eight to one. The uranium- rich CCD overflow is pumped to the clarifier whilst the CCD underflow, with minimal residual uranium, is sent to the Deilmann tailings management facility.

In the solvent extraction plant, the clarified overflow pregnant solution is concentrated and purified by mixing with an organic solvent. The uranium transfers from the aqueous solution to the organic phase leaving behind most of the dissolved impurities. The organic solvent, loaded with uranium, is contacted with ammonium sulphate solution causing the uranium to transfer back to a highly concentrated aqueous phase known as loaded strip solution. A molybdenum removal circuit treats the loaded trip solution to remove molybdenum, an undesirable impurity in the final product.

Using ammonia, uranium is precipitated from the loaded strip solution in the precipitation tank as ammonium diuranate. The precipitate is dewatered in the yellowcake thickener followed by a centrifuge then calcined to U3O8 in a multi-hearth furnace. The final calcined uranium ore concentrate is packed in 200 litre drums for shipment to refineries around the world.