**3. Geochemistry of thorium and thorium minerals**

minerals, such as rutile, zircon, ilmenite, and cassiterite. The principal monazite-producing countries are India, Brazil, Malaysia, and Thailand. Major end uses of thorium are refractories, lamp mantles, and aerospace alloys. Relatively restricted is using thorium in energy production. Although research into thorium-fuelled nuclear reactors continues, there exist no industrial-scale nuclear reactors using thorium. However, India continued its plan for a development of its nuclear power program based on the thorium-fuelled nuclear reactors.

Thorium was identified as an element in the mineral thorite in 1828 by the Swedish chemist Berzelius. Newly discovered element was named for Thor, the Scandinavian God of thunder and lighting, because of its use in energy. In 1885, thorium came into commercial use when it was discovered that a fabric mantle impregnated with a thorium compounds would give a steady, bright white light when heated. This discovery led to the development of the Welsh mantle, which was adopted in gas lighting and later in kerosene lamps. Thorium derived from monazite occurring in the Brazilian beach sands was produced as early as 1885. In 1911,

During this time, the German manufacturers organized a monopoly of the thorium nitrate industry. World War I restricted German supplies of thorium compounds and enabled US production of thorium nitrate to expand. In the early 1920s, electricity began to replace gas and kerosene for general lighting purposes, and the need for thorium mantles declined. Up to the end of World War II, dominate monazite producers were India and Brazil. Since 1945 some other countries have started with their monazite production (e.g., Australia and Malaysia). During World War II started new using of thorium as a component in a high-

After the war, monazite was processed largely for its nuclear fuel potential. The discovery in 1946 that 232Th could be transmuted into 233U increased the interest in thorium. However, the decision to develop nuclear reactors based on uranium fuels slowed development of thorium-fuelled reactors and reduced thorium demand. During the 1950s, some became new producers of thorium, namely Canada and South Africa, where uranium ores from uraniumenriched quartz-pebble conglomerates contain also some thorium. At this time distinctly increased interest in the rare earth elements (REE) and monazite was mined in the first place for its REE content. Some other thorium was also acquired from REE bearing bastnaesite, occurring in carbonate-enriched magmatic rocks (carbonatites). Much of thorium contained

New interest about using thorium as nuclear fuels started in 1960s together with ideas in the development of Fast Breeder Reactors (FBR). Basic research of thorium fuels cycles are being undertaken by Brazil, Germany, the USA, India, Italy, Australia, Canada, China, France, USSR, Romania, and some other countries. Several experimental and prototype nuclear power reactors were successfully operated from the mid-1950s to the mid-1970s

/ThF<sup>4</sup>

Division of the IAEA in this area was supported mainly by organizing some technical

/UF<sup>4</sup>

fuel. The activity of the Nuclear Cycle

monazite from the Indian beach sand deposits mastered world monazite markets.

**2. History**

202 Descriptive Inorganic Chemistry Researches of Metal Compounds

temperature alloys.

using (Th, U)O2

in residues is being stockpiled by private industry [1].

, and LiF/BeF2

, (Th, U)C2

Thorium is widely distributed in nature with an average concentration of 10.5 ppm Th in the upper earth's crust, while the middle crust has an average of 6.5 ppm Th and the lower crust an average of 1.2 ppm Th [7]. Thorium is relatively depleted in mafic igneous rocks (basalts) where the concentration averages about 1 ppm Th, although alkali varieties enriched in Na and K relative to Ca range up to 5 ppm Th. Granitic rocks show a distinct increase over mafic igneous rocks, averaging 20–30 ppm Th. Thorium together with REE could be accumulated during fractional crystallization of alkali igneous rocks. Under some circumstances by this fractionation, a separate carbonate-enriched melt will form, resulting in carbonatites. With carbonatites are associated some complex fluoro-carbonate minerals such as bastnaesite. During weathering, thorium remains in the refractory solid form and is mostly transported as distinct mineral grains (typically as monazite). Sandstones contain about 2 ppm Th, with beach sands containing 10 ppm Th, and limestone averages about 2 ppm. Shale contains 10–15 ppm Th, small amounts of thorium may adsorb clay particles during weathering. Twelve isotopes of thorium are known, with atomic masses from 223 to 234. However, natural thorium is present as nearly 100% 232Th isotope. The other important natural isotope of thorium 230Th is generally presented in uranium minerals.

In general, thorium occurs in relative small number of Th-enriched minerals: thorite (ThSiO<sup>4</sup> ), thorianite (ThO2 ), monazite [(Ce, La, Nd,Th,U)PO<sup>4</sup> ], bastnaesite [(Ce, La)CO3 F], and thorogummite [Th(SiO<sup>4</sup> ) 1−x(OH)4−x]. However, the main world resources of thorium are coupled with monazite and bastnaesite. Monazite is a primary source of light REE. Monazite concentrates, which are mined from beach sands in India, Brazil, the USA, Malaysia, Korea, and Sri Lanka, contain 3.1–14.32 wt.% ThO<sup>2</sup> and 40.7–65.0 wt.% REO (rare earths oxides). However, monazites from some granitic rocks could contain up to 27 wt.% ThO2 .

Other, especially, potentially based resources of thorium are coupled with carbonateenriched magmatic rocks (carbonatites), containing bastnaesite (up to 2.8 wt.% ThO<sup>2</sup> ), parisite [CaREE2 (CO3 )3 (F,OH)2 ] (up to 4.0 wt.% ThO<sup>2</sup> ), and synchysite [CaREE(CO3 )2 (F, OH)] (up to 5.0 wt.% ThO2 ). Highly rare alkali-rich nephelinite syenites from the Lovozero pluton on the Kola peninsula (Russia) contain rare REE-enriched mineral loparite (Na,REE,Ca) (Ti, Nb) O2 with up to 1.6 wt.% ThO2 [8]. Some higher concentrations of thorium have also important apatite ore deposit on the Kola Peninsula in the Russia. Apatite containing higher concentrations of thorium occurs also in the alkalic magmatic rocks on the Vishnevyye Mountains of the Urals range in the Russia [1]. A large variety of other minerals contain minor amounts of thorium (e.g., allanite, xenotime, zircon, and uraninite).
