HKNIC - Mining and Milling

Mining and Milling

Uranium is the basic raw material for nuclear power. Naturally occurring exploitable uranium ore may contain as little as 0.1% uranium, in the form of an oxide or silicate.

Mining of uranium is carried out either by excavation or by “in-situ leaching” or ISL. Excavation, the traditional method, involves either open-cast or underground mining. With ISL,which allows extraction from very low grade ores with very minor surface disturbance, oxygenated ground water containing a slightly acidic or alkaline solution is circulated through a porous body of ore to dissolve the uranium and bring it to the surface in a “well”. The uranium is then recovered from the solution in a conventional mill. In 2006, about half the uranium was mined at open pits, with underground mining and ISL accounting for about a quarter each.

Milling typically takes place in a mill located close to the mine. In a mill, the solid ore is ground down and the uranium extracted by leaching using a strong acid or alkaline solution to dissolve the uranium. The uranium is chemically recovered from this solution and then precipitated and dried. The precipitate occurs mainly as a bright yellow uranium oxide concentrate referred to as “yellowcake.” It contains typically 60%-80% uranium. With ISL, a uranium compound is recovered from the solution extracted from the production well through a process known as ion exchange, to be converted again to a uranium oxide.

After excavation, the remainder of the uranium ore, or “tailing”, which contains most of the radioactivity and the rock material, needs to be placed and capped in engineered dams or back-filled in mines to isolate it from the environment. There is far less disturbance with ISL. Simply capping the boreholes and replanting over any evaporation ponds is generally sufficient to isolate any radioactivity.

Mining and Milling
Uranium mining process
Mining and Milling