Jump to content

Thorium: Difference between revisions

Edit links
From Wikipedia, the free encyclopedia
Browse history interactively
← Previous editNext edit →
Content deleted Content added
VisualWikitext
Line 177: Line 177:
*[http://www.uic.com.au/ The Uranium Information Centre] provided some of the original material in this article.
*[http://www.uic.com.au/ The Uranium Information Centre] provided some of the original material in this article.
*[http://www.euronuclear.org/info/encyclopedia/d/decaybasinnatural.htm European Nuclear Society — Natural Decay Chains]
*[http://www.euronuclear.org/info/encyclopedia/d/decaybasinnatural.htm European Nuclear Society — Natural Decay Chains]
*[http://www.acceleratingfuture.com/michael/blog/2006/10/a-nuclear-reactor-in-every-home/ an article by Michael Annismov advocating dopting Thorium reactors]
*[http://www.acceleratingfuture.com/michael/blog/2006/10/a-nuclear-reactor-in-every-home/ often-quoted article by Michael Annissimov advocating dopting Thorium reactors]


==External links==
==External links==

Revision as of 11:18, 14 December 2008

Thorium, 90Th
Small (3 cm) ampule with a tiny (5 mm) square of metal in it
Thorium
Pronunciation/ˈθɔːriəm/ ​(THOR-ee-əm)
Appearancesilvery
Standard atomic weight Ar°(Th)
Thorium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Ce
↑
Th
↓
—
actinium ← thorium → protactinium
Atomic number (Z)90
Groupf-block groups (no number)
Periodperiod 7
Block  f-block
Electron configuration[Rn] 6d2 7s2
Electrons per shell2, 8, 18, 32, 18, 10, 2
Physical properties
Phase at STPsolid
Melting point2023 K ​(1750 °C, ​3182 °F)
Boiling point5061 K ​(4788 °C, ​8650 °F)
Density (at 20° C)11.725 g/cm3 [3]
Heat of fusion13.81 kJ/mol
Heat of vaporization514 kJ/mol
Molar heat capacity26.230 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 2633 2907 3248 3683 4259 5055
Atomic properties
Oxidation statescommon: +4
−1,[4] +1,? +2,[5] +3[5]
ElectronegativityPauling scale: 1.3
Ionization energies
  • 1st: 587 kJ/mol
  • 2nd: 1110 kJ/mol
  • 3rd: 1930 kJ/mol
Atomic radiusempirical: 179.8 pm
Covalent radius206±6 pm
Color lines in a spectral range
Spectral lines of thorium
Other properties
Natural occurrenceprimordial
Crystal structure ​face-centered cubic (fcc) (cF4)
Lattice constant
Facecentredcubic crystal structure for thorium
a = 508.45 pm (at 20 °C)[3]
Thermal expansion11.54×10−6/K (at 20 °C)[3]
Thermal conductivity54.0 W/(m⋅K)
Electrical resistivity157 nΩ⋅m (at 0 °C)
Magnetic orderingparamagnetic[6]
Molar magnetic susceptibility132.0×10−6 cm3/mol (293 K)[7]
Young's modulus79 GPa
Shear modulus31 GPa
Bulk modulus54 GPa
Speed of sound thin rod2490 m/s (at 20 °C)
Poisson ratio0.27
Mohs hardness3.0
Vickers hardness295–685 MPa
Brinell hardness390–1500 MPa
CAS Number7440-29-1
History
Namingafter Thor, the Norse god of thunder
DiscoveryJöns Jakob Berzelius (1829)
Isotopes of thorium
Main isotopes[8] Decay
abun­dance half-life (t1/2) mode pro­duct
227Th trace 18.68 d α 223Ra
228Th trace 1.9116 y α 224Ra
229Th trace 7917 y[9] α 225Ra
230Th 0.02% 75400 y α 226Ra
231Th trace 25.5 h β− 231Pa
232Th 100.0% 1.405×1010 y α 228Ra
233Th trace 21.83 min β− 233Pa
234Th trace 24.1 d β− 234Pa
 Category: Thorium
| references

Thorium (Template:PronEng) is a chemical element with the symbol Th and atomic number 90. As a naturally occurring, slightly radioactive metal, it has been considered as an alternative nuclear fuel to uranium.

Characteristics

When pure, thorium is a silvery-white metal that retains its luster for several months. However, when it is exposed to oxygen, thorium slowly tarnishes in air, becoming grey and eventually black. Thorium dioxide (ThO2), also called thoria, has the highest melting point of any oxide (3300°C).[10] When heated in air, thorium metal turnings ignite and burn brilliantly with a white light.

Thorium has the largest liquid range of any element: 2946 K between the melting point and boiling point.

See Actinides in the environment for details of the environmental aspects of thorium.

Applications

Applications of thorium:

Applications of thorium dioxide (ThO2):

History

M. T. Esmark found a black mineral on Løvøy Island, Norway and gave a sample to Professor Jens Esmark, a noted mineralogist who was not able to identify it, so he sent a sample to the Swedish chemist Jöns Jakob Berzelius for examination in 1828.[11] Berzelius analysed it and named it after Thor, the Norse god of thunder. The metal had virtually no uses until the invention of the gas mantle in 1885.

Between 1900 and 1903, Ernest Rutherford and Frederick Soddy showed how thorium decayed at a fixed rate over time into a series of other elements. This observation led to the identification of half life as one of the outcomes of the alpha particle experiments that led to their disintegration theory of radioactivity.[12]

The crystal bar process (or Iodide process) was discovered by Anton Eduard van Arkel and Jan Hendrik de Boer in 1925 to produce high-purity metallic thorium.[13]

The name ionium was given early in the study of radioactive elements to the 230Th isotope produced in the decay chain of 238U before it was realized that ionium and thorium were chemically identical. The symbol Io was used for this supposed element.

Occurrence

Monazite, a rare-earth-and-thorium phosphate mineral, is the primary source of the world's thorium

Thorium is found in small amounts in most rocks and soils, where it is about three times more abundant than uranium, and is about as common as lead. Soil commonly contains an average of around 12 parts per million (ppm) of thorium. Thorium occurs in several minerals, the most common being the rare-earth thorium-phosphate mineral monazite, which may contain up to about 12% thorium oxide. Thorium-containing monazite(Ce) occurs in Africa, Antarctica, Australia, Europe, India, North America, and South America.[14]

232Th decays very slowly (its half-life is about three times the age of the earth) but other thorium isotopes occur in the thorium and uranium decay chains. Most of these are short-lived and hence much more radioactive than 232Th, though on a mass basis they are negligible.

See also thorium minerals.

Distribution

Present knowledge of the distribution of thorium resources is poor because of the relatively low-key exploration efforts arising out of insignificant demand.[15] There are two sets of estimates that define world thorium reserves, one set by the US Geological Survey (USGS) and the other supported by reports from the OECD and the International Atomic Energy Agency (the IAEA). Under the USGS estimate, Australia and India have particularly large reserves of thorium. India and Australia are believed to possess approx 300,000 metric tonnes each; i.e. each country possessing 25% of the world's thorium reserves.[16] However, in the OECD reports, estimates of Australian's Reasonably Assured Reserves (RAR) of Thorium indicate only 19,000 metric tonnes and not 300,000 tonnes as indicated by USGS. The two sources vary wildly for countries such as Brazil, Turkey, and Australia. However, both reports appear to show some consistency with respect to India's thorium reserve figures, with 290,000 metric tonnes (USGS) and 319,000 metric tonnes (OECD/IAEA). Furthermore the IAEA report mentions that India possesses two thirds (67%) of global reserves of monazite, the primary thorium ore:

The world’s reserve of monazite is estimated to be in the range of 12 million tonnes of which nearly 8 million tonnes occur with the heavy minerals in the beach sands of India in the States of Kerala, Tamil Nadu, Andhra Pradesh and Orissa.

[17]

The IAEA also states that recent reports have upgraded India's thorium deposits up from approximately 300,000 metric tonnes to 650,000 metric tonnes:

In the RAR category, the deposits in Brazil, Turkey and India are in the range of 0.60, 0.38 and 0.32 million tonnes respectively. The thorium deposits in India has recently been reported to be in the range 0.65 million tonnes.

[18]

Therefore, the IAEA and OECD appear to conclude that Brazil and India may actually possess the lion's share of world's thorium deposits.


  • The prevailing estimate of the economically available thorium reserves comes from the US Geological Survey, Mineral Commodity Summaries (1997-2006):[19][20]
Country Th Reserves (tonnes)     Th Reserve Base (tonnes)
Australia 300,000           340,000          
India 290,000 300,000
Norway 170,000 180,000
United States 160,000 300,000
Canada 100,000 100,000
South Africa 35,000 39,000
Brazil 16,000 18,000
Malaysia 4,500 4,500
Other Countries 95,000 100,000
World Total 1,200,000 1,400,000

Note: The Australian figures are based on assumptions and not on actual geological surveys, therefore the figures cited for Australia may be misleading, should be treated with caution and could possibly indicate inflated values for Australia's actual reserves of thorium; note the OECD estimates of Australian's Reasonably Assured Reserves (RAR) of Thorium (listed below) indicate only 19,000 metric tonnes and not 300,000 tonnes as listed above.

  • Another estimate of Reasonably Assured Reserves (RAR) and Estimated Additional Reserves (EAR) of thorium comes from OECD/NEA, Nuclear Energy, "Trends in Nuclear Fuel Cycle", Paris, France (2001).[21]
Country RAR Th (tonnes)   EAR Th (tonnes)
Brazil 606,000           700,000          
Turkey 380,000 500,000
India 319,000     —
United States 137,000 295,000
Norway 132,000 132,000
Greenland 54,000 32,000
Canada 45,000 128,000
Australia 19,000     —
South Africa 18,000     —
Egypt 15,000 309,000
Other Countries   505,000     —
World Total 2,230,000 2,130,000

Thorium as a nuclear fuel

Main article: Thorium fuel cycle

Thorium, as well as uranium and plutonium, can be used as fuel in a nuclear reactor. Although not fissile itself, 232Th will absorb slow neutrons to produce 233U, which is fissile. Hence, like 238U, it is fertile.

Problems include the high cost of fuel fabrication due partly to the high radioactivity of 233U which is a result of its contamination with traces of the short-lived 232U; the similar problems in recycling thorium due to highly radioactive 228Th; some weapons proliferation risk of 233U; and the technical problems (not yet satisfactorily solved) in reprocessing. Much development work is still required before the thorium fuel cycle can be commercialised, and the effort required seems unlikely while (or where) abundant uranium is available.

Nevertheless, the thorium fuel cycle, with its potential for breeding fuel without fast neutron reactors, holds considerable potential long-term benefits. Thorium is significantly more abundant than uranium, and is a key factor in sustainable nuclear energy. Perhaps more importantly, thorium produces several orders of magnitude less long-lived radioactive waste.

One of the earliest efforts to use a thorium fuel cycle took place at Oak Ridge National Laboratory in the 1960s. An experimental reactor was built based on molten salt reactor technology to study the feasibility of such an approach, using thorium-fluoride salt kept hot enough to be liquid, thus eliminating the need for fabricating fuel elements. This effort culminated in the Molten-Salt Reactor Experiment that used 232Th as the fertile material and 233U as the fissile fuel. Due to a lack of funding, the MSR program was discontinued in 1976.


In 2007, Norway was debating whether or not to focus on thorium plants, due to the existence of large deposits of thorium ores in the country, particularly at Fensfeltet, near Ulefoss in Telemark county.

The primary fuel of the HT3R Project near Odessa, Texas, USA will be ceramic-coated thorium beads.

Isotopes

Main article: isotopes of thorium

Naturally occurring thorium is composed of one isotope: 232Th. Twenty-seven radioisotopes have been characterized, with the most abundant and/or stable being 232Th with a half-life of 14.05 billion years, 230Th with a half-life of 75,380 years, 229Th with a half-life of 7340 years, and 228Th with a half-life of 1.92 years. All of the remaining radioactive isotopes have half-lives that are less than thirty days and the majority of these have half-lives that are less than ten minutes. One isotope, 229Th, has a nuclear isomer (or metastable state) with a remarkably low excitation energy of 7.6 eV.[22]

The known isotopes of thorium range in atomic weight from 210 u (210Th) to 236 u (236Th).[23]

Precautions

Powdered thorium metal is often pyrophoric and should be handled carefully.

Natural thorium decays very slowly compared to many other radioactive materials, and the alpha radiation emitted cannot penetrate human skin. Owning and handling small amounts of thorium, such as a gas mantle, is considered safe if care is taken not to ingest the thorium -- lungs and other internal organs can be penetrated by alpha radiation. Exposure to an aerosol of thorium can lead to increased risk of cancers of the lung, pancreas and blood. Exposure to thorium internally leads to increased risk of liver diseases. This element has no known biological role. See also Thorotrast.

Thorium extraction

Thorium has been extracted chiefly from monazite through a multi-stage process. In the first stage, the monazite sand is dissolved in an inorganic acid such as sulfuric acid (H2SO4). In the second, the Thorium is extracted into an organic phase containing an amine. Next it is separated or "stripped" using an ion such as nitrate, chloride, hydroxide, or carbonate, returning the thorium to an aqueous phase. Finally, the thorium is precipitated and collected.[24]

See also

Footnotes

  1. ^ "Standard Atomic Weights: Thorium". CIAAW. 2013.
  2. ^ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
  3. ^ a b c Arblaster, John W. (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. ISBN 978-1-62708-155-9.
  4. ^ Th(-I) and U(-I) have been detected in the gas phase as octacarbonyl anions; see Chaoxian, Chi; Sudip, Pan; Jiaye, Jin; Luyan, Meng; Mingbiao, Luo; Lili, Zhao; Mingfei, Zhou; Gernot, Frenking (2019). "Octacarbonyl Ion Complexes of Actinides [An(CO)8]+/− (An=Th, U) and the Role of f Orbitals in Metal–Ligand Bonding". Chemistry (Weinheim an der Bergstrasse, Germany). 25 (50): 11772–11784. 25 (50): 11772–11784. doi:10.1002/chem.201902625. ISSN 0947-6539. PMC 6772027. PMID 31276242.
  5. ^ a b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 28. ISBN 978-0-08-037941-8.
  6. ^ Lide, D. R., ed. (2005). "Magnetic susceptibility of the elements and inorganic compounds". CRC Handbook of Chemistry and Physics (PDF) (86th ed.). CRC Press. pp. 4–135. ISBN 978-0-8493-0486-6.
  7. ^ Weast, R. (1984). CRC, Handbook of Chemistry and Physics. Chemical Rubber Company Publishing. p. E110. ISBN 978-0-8493-0464-4.
  8. ^ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
  9. ^ Varga, Z.; Nicholl, A.; Mayer, K. (2014). "Determination of the 229Th half-life". Physical Review C. 89 (6): 064310. doi:10.1103/PhysRevC.89.064310.
  10. ^ Emsley, John (2001). Nature's Building Blocks ((Hardcover, First Edition) ed.). Oxford University Press. p. 441. ISBN 0198503407.
  11. ^ "Thorium". BBC.co. Retrieved 2007-01-18.
  12. ^ Simmons, John Galbraith (1996). The Scientific 100. Seacaucus NJ: Carol. p. 19.
  13. ^ van Arkel, A.E. (1925). "Preparation of pure titanium, zirconium, hafnium, and thorium metal". Zeitschrift für Anorganische und Allgemeine Chemie. 148: 345–350. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  14. ^ Monazite-(Ce): Monazite-(Ce) mineral information and data
  15. ^ K.M.V. Jayaram. "An Overview of World Thorium Resources, Incentives for Further Exploration and Forecast for Thorium Requirements in the Near Future" (PDF).
  16. ^ "US approves Indian nuclear deal". BBC News. 2006-12-09.
  17. ^ IAEA: Thorium fuel cycle — Potential benefits and challenges (PDF). p. 45.
  18. ^ IAEA: Thorium fuel cycle — Potential benefits and challenges (PDF). p. 45.
  19. ^ "U.S. Geological Survey, Mineral Commodity Summaries - Thorium".
  20. ^ "Information and Issue Briefs - Thorium". World Nuclear Association. Retrieved 2006-11-01.
  21. ^ IAEA: Thorium fuel cycle — Potential benefits and challenges (PDF). pp. 45(table 8), 97(ref 78).
  22. ^ Phys. Rev. Lett. 98 142501 (April 2007)
  23. ^ Phys. Rev. C 52, 113–116 (1995)
  24. ^ Crouse, David; Brown, Keith (December 1959) "The Amex Process for Extracting Thorium Ores with Alkyl Amines".Industrial & Engineering Chemistry 51 (12): 1461. Retrieved on 2007-03-09

References

Wikimedia Commons has media related to Thorium.
Look up thorium in Wiktionary, the free dictionary.
Retrieved from "https://en.wikipedia.org/enwiki/w/index.php?title=Thorium&oldid=257887779"