Thorium is a radioactive metal in the actinide series. As a fertile material, it has been considered an alternative to uranium in nuclear fuel, and thorium is three times as abundant as uranium. Thorium dioxide has the highest melting point of any oxide. The primary source of thorium is the mineral monazite. An isomer of thorium-239 has an excitation energy near optical energy, and it might be possible to use a laser to turn the decay on and off.
Domestic Production and Use: The primary source of the world’s thorium is the rare-earth and thorium phosphate mineral monazite. In the United States, thorium has been a byproduct of refining monazite for its rare-earth content. Monazite itself is recovered as a byproduct of processing heavy-mineral sands for titanium and zirconium minerals. In 2010, monazite was not recovered domestically as a salable product. Essentially all thorium compounds and alloys consumed by the domestic industry were derived from imports, stocks of previously imported materials, or materials previously shipped from U.S. Government stockpiles. About eight companies processed or fabricated various forms of thorium for nonenergy uses, such as catalysts, high-temperature ceramics, and welding electrodes. Thorium’s use in most products has generally decreased because of its naturally occurring radioactivity. The value of thorium compounds used by the domestic industry was estimated to have decreased to $174,000 from $275,000 in 2009.
Import Sources (2006–09): Monazite: United Kingdom, 72%; Canada, 28%. Thorium compounds: United Kingdom, 76%; France, 20%; India, 2%; and Canada, 2%.
Depletion Allowance: Monazite, 22% on thorium content, 14% on rare-earth and yttrium content (Domestic); 14% (Foreign).
Government Stockpile: None.
Events, Trends, and Issues: Domestic mine production of thorium-bearing monazite ceased at the end of 1994 as world demand for ores containing naturally occurring radioactive thorium declined. Imports and existing stocks supplied essentially all thorium consumed in the United States in 2010. Domestic demand for thorium ores, compounds, metals, and alloys has exhibited a long-term declining trend. There were exports and domestic shipments of thorium material in the United States in 2010, according to the U.S. Census Bureau and the U.S. Geological Survey, respectively. In 2010, unreported thorium consumption was believed to be primarily in catalysts, microwave tubes, and optical equipment and was estimated to have increased.
Increased costs to monitor and dispose of thorium have caused domestic processors to switch to thorium-free materials. Real and potential costs related to compliance with State and Federal regulations, proper disposal, and monitoring of thorium’s radioactivity have limited its commercial value. It is likely that thorium’s use will continue to decline unless a low-cost disposal process is developed or new technology, such as a nonproliferative nuclear fuel, creates renewed demand.
On the basis of data through September 2010, the average value of imported thorium compounds decreased to $67.65 per kilogram from the 2009 average of $122.56 per kilogram (gross weight). The average value of exported thorium compounds increased to $371.00 per kilogram based on data through September 2010, compared with $96.55 for 2009.
World Refinery Production and Reserves: Reserves are contained primarily in the rare-earth ore mineral monazite and the thorium mineral thorite. Without demand for the rare earths, monazite would probably not be recovered for its thorium content. Other ore minerals with higher thorium contents, such as thorite, would be more likely sources if demand significantly increased. New demand is possible with the development and testing of thorium nuclear fuel in Russia and India. Reserves exist primarily in recent and ancient placer deposits and in thorium vein deposits, especially those in the Lemhi Pass area of Idaho. Lesser quantities of thorium-bearing monazite and thorite reserves occur in certain iron ore deposits and carbonatites. Thorium enrichment in iron ore is known in iron (Fe)-REE-thorium-apatite (FRETA) deposits, similar to the FRETA deposits in Mineville, NY, Pea Ridge, MO, and Scrub Oaks, NJ.
World Resources: Thorium resources occur in geologic provinces similar to those that contain reserves. The leading share is contained in placer deposits. Resources of more than 500,000 tons are contained in placer, vein, and carbonatite deposits. Disseminated deposits in various other alkaline igneous rocks contain additional resources of more than 2 million tons. Large thorium resources are found in Australia, Brazil, Canada, Greenland (Denmark), India, South Africa, and the United States.
Substitutes: Nonradioactive substitutes have been developed for many applications of thorium. Yttrium compounds have replaced thorium compounds in incandescent lamp mantles. A magnesium alloy containing lanthanides, yttrium, and zirconium can substitute for magnesium-thorium alloys in aerospace applications.
(wiki) - Thorium on Wikipedia
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