A piece of ore containing metallic uranium. (photo by chief scientist Li Ziying)
A geological team recently discovered the existence of natural metallic uranium in China, disproving a belief it could only exist as a compound naturally, thus requiring extraction treatment.
The team from Beijing Research Institute of Uranium Geology at China National Nuclear Corporation have found ores containing metallic uranium in northern Guangdong Province, and published their findings in the latest edition of Acta Geologica Sinica, a Chinese official academic journal on geology published in English.
Chief scientist Li Ziying said the research team analyzed the natural pitchblende, a dark-colored form of the mineral uraninite, in the hydrothermal uranium deposits common to southern China. In a comparative analysis between the lab-extracted metallic uranium and the oxidation-reduction (redox) uranium, they confirmed the existence of the zero-valence metallic uranium in a natural environment.
This confirmed suspicions regarding its existence as early as 2011, according to a team member named Huang Zhizhang.
Uranium is an important raw material for nuclear energy. U-235, one of its three isotopes, is extensively used in the nuclear industry and for military purposes in the development of nuclear weapons.
Uranium has a highly active chemical nature and is extremely volatile. This is why the element mostly exists in the form of a compound in the natural environment.
Huang Zhizhang, an expert in his late 70's, explained that the discovery started with the team's research on an established international theory that the "tetravalent compound containing uranium found near the earth surface was a result of reduction from the hexavalent uranium carried by ore-bearing hydrothermal solution from deeper inside the earth's core.
However, the team gradually came to believe that hexavalent uranium was unlikely to exist at a lower level than the tetravalent compound because the closer to the earth's center, the less oxygen there is. Therefore, deep inside the earth, the uranium element should exist in the form of zero-valence, i.e. the metallic form.
Finding natural metallic uranium does not mean any direct application on a large industrial scale because turning uranium into nuclear fuel still requires extraction and enrichment of the U-235 isotope in the ore. Therefore, natural metallic uranium cannot at present replace synthetic uranium.
However, the finding's significance is that it provides evidence of the hydrothermal uranium mineralization mechanism, and the evolution of geothermal energy apart from digging deeper to richer uranium ores.
