Thorium is a weak radioactive element of the actinide series. It is chemically represented as Th with an atomic number of 90 and atomic weight of 232.03. It is inherently unstable; all of its isotopes are radioactive. The only stable known isotope is 232Th, which is metal and has half-life of equivalent to that of the universe -14.05 billion years. This is significant because it is one of the only two naturally occurring actinides, Uranium being the other. Since Thorium occurs naturally, it can be mined, and its radioactive properties harnessed. Thorium decays through alpha decay and it is very slow. The decay chain is known as thorium series that will result in a stable 208Pb.
List of Countries by Thorium Reserves
Largest Thorium Reserves
At present, information on resources of thorium ores is low since its low economic potential renders widespread exploration unnecessary. The main sources of information on thorium reserves are USGS (United States Geological Survey) and the IAEA (International Atomic Energy Agency). IAEA and USGS figures agree the largest reserves in the world are found in India which has around 25% of the world reserves, currently estimated at 519,000 tons. India plans to use its reserve as a cornerstone in its energy independence plans.
USGS figures put the US and Australia's reserves at par with India, however, according to the IAEA, Australia has 489,000 tons which represents 19% of the world reserves. Australia's government estimates its RAR (Reasonably Assured Reserves) at only 19,000 tons. The United States has the third largest reserves are in the world, which is estimated to be about 400 thousand tons or 13% of the world reserves.
The same disparity exists for figures given by the two bodies for Turkey and Brazil with USGS figures being higher than IAEA estimates. Turkey’s total reserves is estimated to be about 344,000 tons or 11% of the world reserves. Venezuela and Brazil are two countries estimated each having 302,000 tons representing a total of 20% of the world reserves.
What is Thorium Used For?
Thorium Oxide (thoria) has a melting point of 5,972 degrees Fahrenheit which is one of the highest known for a stable compound. ThO2, the chemical formula of thorium oxide, has accordingly found use in a high-temperature application. Some of its uses are in heat resistant crucibles, arc lighting elements, high-intensity lanterns, and arc-welding. Thorium is also used in high-end magnification lens used in scientific and photographic equipment due to its excellent wavelength dispersion and refractive index. As a radioactive element, thorium has been used in weapon and energy production. The US experimented with thorium-based fission bombs in mid-1950's, but they did not go into production as they were hard to store and were easily detected. Use of thorium in energy generation was reported by the US in 1962 when the Indian Point Energy Center In New York reactor started producing power. However, the use of thorium was short lived as the reactor was switched to uranium oxide.
Currently, there are no mines that exclusively or primarily mine thorium since global demand is low, ranging from a few tens of tons a year. Thorium is mainly mined from different minerals like thorite, thorianite, and monazite which is a by-product of mining of rare earth minerals.