Open Pit Mining:
Open pit mining is often used in areas where ore bodies are not far below the surface (usually within 400ft below the surface). Various excavation techniques are used to remove the overlying rock, called the overburden, which allow miners to manually extract the uranium ore using machinery. Open pit mining is less expensive than other methods but it leaves a huge surface footprint as can be seen in this picture of the Rössing Uranium Mine in Namibia.
When the uranium deposit is too far below the surface for open pit mining, underground mining must be used to reach the ore bodies. Underground mining involves the construction of access shafts and tunnels up to about 600 meters deep. The ore is drilled into and sometimes blasted to create debris that is then collected and transported to the surface. While this process creates less of a footprint on the surface of the earth, it is more expensive than open pit mining and can potentially impact local aquifers.
When ore bodies exist within groundwater or in non-rock soils such as sand or gravel, in-situ recovery methods are used. Instead of excavating the ore, the in-situ process is rather complex. The existing groundwater is mixed with an oxidant such as gaseous oxygen and a baking soda solution that separates the uranium from the porous soil before it is pumped to the surface (refer to the diagram below). While in-situ recovery has a small surface footprint and little waste rock, possible contamination of aquifers is possible.
Future Research: Seawater Extraction
Uranium exists in very low concentrations in seawater. However, with the amount of water on this planet it is estimated that there is about a thousand times more uranium dissolved in seawater than in conventional underground deposits. Thus far, research into extracting uranium from seawater has been promising, but certainly extraction levels are not yet high enough to discuss the end of conventional and in-situ mining techniques.
In the next segment of Nuclear 101, we will discuss the process of uranium milling in which extracted uranium, from the mining processes described above, is processed into a usable material called “yellowcake.”
Gamma ray Spectrometry
GeoInfo: NM Bureau of Geology
HSW: Uranium Mining
World Nuclear Association (1)
World Nuclear Association (2)