Don't Eat the Yellowcake: Uranium Mining

There are a lot of us out there that don't exactly understand the processes behind "mining" uranium. It's actually a lot like the mining processes for other materials. People seem to have this notion that uranium is a very rare commodity when actually the earth's crust has about a 2.8 parts per million concentration of uranium, about the same as tin. My expertise is actually in the metallurgy field which is greatly connected with mining, so I want to take the time to clear up some misconceptions (hopefully) and explain just how uranium is mined.

There are three main types of uranium mines out there: In Situ, Open pit /underground, and heap leaching.

In Situ leaching (or solution mining) of uranium can be used if an orebody lies in some type of porous material and in ground water. Bore holes are drilled through the ore body and subsequently a leaching solution is poured down the bore holes. Once the leaching solution comes into contact with the ore body it dissolves the wanted material and thus when it is pumped back up to the surface the solution now contains uranium. The uranium is then recovered as a precipitate. Common leaching solutions used for uranium are sulfuric acid or sodium bicarbonate (but others can be used). One benefit of in situ leaching is that it has little ground disturbance (vs. open pit/underground mining) and there is no need for crushing.

Open pit and underground mining of uranium is pretty self explanatory (it's probably the picture that comes to mind when we all think of "mining"). If the uranium deposits are located somewhat close to the surface then open pit mining is preferential. A large pit is made and piles of ground material (uranium plus the rock material) are removed and sent to a processing/separation facility. All of the material will be crushed and then leached with an acid in order to dissolve the uranium oxides. Once uranium oxides are dried out (85% uranium by mass at this point) the resulting product is what we all know as "yellowcake". This is then packed into steel drums and sent to where they are needed. Underground mining is generally the same expect for the uranium deposits sit deeper within the crust and so tunnels must be dug into the ground in order to mine the uranium. These two options are by far the most popular, they account for 57% of the uranium mines.

Finally, heap leaching is very similar to in situ leaching. Except now very low grade ore is piled up and acid is poured on it. The new solution with dissolved uranium is then collected from underneath the pile and processed in the same way as with in situ.

So where is this being done? Turns out that there are uranium mines in over twenty countries. However, the top six of these countries produce about 85% of the mined uranium. They are: Kazakhstan, Canada, Australia, Namibia, Russia, and Niger in that order (but Australia has by far the largest reserves). In 2009 approximately 60,000 tonnes of uranium were mined which met 76% of the world's demands at the time. One good thing is that it is actually relatively simple to find uranium sources...considering the element is radioactive. A map of a region's radioactivity can be made and thus uranium can be found.

Well, is it safe? In fact...it is. Because the uranium is in such a low concentration there are no major health concerns for workers in the mine. There are however, a few uranium mines that deal with high concentrations. In these rare cases, special measures are taken to ensure that uranium dust does not get into the air and there is limited contact with the actual ore.

These methods have been used for decades and I don't see them changing anytime soon. It works and so it will continue. However, the search for better leachants and solutions is always on in order to recover more of the uranium.