- Main article: isotope geochemistry
3He is a primordial substance in the Earth's mantle, considered to have become entrapped within the Earth during planetary formation. The ratio of 3He to 4He within the Earth's crust and mantle is less than that for assumptions of solar disk composition as obtained from meteorite and lunar samples, with terrestrial materials generally containing lower 3He/4He ratios due to ingrowth of 4He from radioactive decay.
3He is present within the mantle, in the ratio of 200-300 parts of 3He to a million parts of 4He. Ratios of 3He/4He in excess of atmospheric are indicative of a contribution of 3He from the mantle. Crustal sources are dominated by the 4He which is produced by the decay of radioactive elements in the crust and mantle.
The ratio of Helium-3 to Helium-4 in natural Earth-bound sources varies greatly. Samples of the ore Spodumene from Edison Mine, South Dakota were found to contain 12 parts of He-3 to a million parts of Helium-4. Samples from other mines showed 2 parts per million.
Helium is also present as up to 7% of some natural gas sources, and large sources have over 0.5 percent (above 0.2 percent makes it viable to extract). Algeria's annual gas production is assumed to contain 100 million normal cubic metres and this would contain between 5 and 50 m3 of Helium-3 (about 1 to 10 kilograms) using the normal abundance range of 0.5 to 5 ppm. Similarly the US 2002 stockpile of 1 billion normal m3 would have contained about 10 to 100 kilograms of He-3.
3He is also present in the Earth's atmosphere. The natural abundance of 3He in naturally occurring helium gas is 1.38×10-6 (1.38 parts per million). The partial pressure of helium in the Earth's atmosphere is about 4 millitorr, and thus helium accounts for 5.2 parts per million of the total pressure (760 torr) in the Earth's atmosphere, and 3He thus accounts for 7.2 parts per trillion of the atmosphere. Since the atmosphere of the Earth has a mass of about 5.14 x 1015metric tons, the mass of 3He in the Earth's atmosphere is the product of these numbers, or 37,000 tons of 3He.
3He is produced on Earth from three sources: lithium spallation, cosmic rays, and beta decay of tritium (3H). The contribution from cosmic rays is negligible within all except the oldest regolith materials, and lithium spallation reactions are a lesser contributor than the production of 4He by alpha particle emissions.
Template:RelevanceThe total amount of helium-3 in the mantle may be in the range of 100 thousand to a million tonnes. However, this mantle helium is not directly accessible.Template:Clarify me Some of it leaks up through deep-sourced hotspot volcanoes such as those of the Hawaiian islands, but only 300 grams per year is emitted to the atmosphere. Mid-ocean ridges emit another 3 kilogram per year. Around subduction zones, various sources produce helium-3 in natural gas deposits which possibly contain a thousand tonnes of helium-3 (although there may be 25 thousand tonnes if all ancient subduction zones have such deposits). Wittenberg estimated that United States crustal natural gas sources may have only half a tonne total. Wittenberg cited Anderson's estimate of another 1200 metric tonnes in interplanetary dust particles on the ocean floors. In the 1994 study, extracting helium-3 from these sources consumes more energy than fusion would release. Wittenberg also writes that extraction from US crustal natural gas, consumes ten times the energy available from fusion reactions.Template:Clarify me
Due to the rarity of helium-3 on Earth, it is manufactured instead of recovered from natural deposits. Helium-3 is a byproduct of tritium decay, and tritium can be produced through neutron bombardment of lithium, boron, or nitrogen targets. Current supplies of helium-3 come, in part, from the dismantling of nuclear weapons where it accumulates; approximately 150 kilograms of it have resulted from decay of US tritium production since 1955, most of which was for warheads. However, the production and storage of huge amounts of the gas tritium is probably uneconomical, as tritium must be produced at the same rate as helium-3, and roughly eighteen times as much of tritium stock is required as the amount of helium-3 produced annually by decay (production rate dN/dt from number of moles or other unit mass of tritium N, is N γ = N ln 2/t½ where the value of t½/(ln 2) is about 18 years; see radioactive decay). If commercial fusion reactors were to use helium-3 as a fuel, they would require tens of tons of helium-3 each year to produce a fraction of the world's power, implying need for the same amount of new tritium production, as well as the need to keep 18 times this figure in total tritium breeder stocks. Breeding tritium with lithium-6 consumes the neutron, while breeding with lithium-7 produces a low energy neutron as a replacement for the consumed fast neutron. Note that any breeding of tritium on Earth requires the use of a high neutron flux, which proponents of helium-3 nuclear reactors hope to avoid.
Tritium occurs naturally due to cosmic rays interacting with atmospheric gases. In the most important reaction for natural tritium production, a fast neutron (greater than 4MeV) interacts with atmospheric nitrogen:
Because of tritium's relatively short half-life, however, tritium produced in this manner does not accumulate over geological timescales, and its natural abundance is negligible.
Tritium is produced in nuclear reactors by neutron activation of lithium-6. This is possible with neutrons of any energy, and is an exothermic reaction yielding 4.8 MeV, which is more than one-quarter of the energy that fusion of the produced triton with a deuteron can later produce.
63Li + n → 42He ( 2.05 MeV ) + Expression error: Unrecognised punctuation character "[".1T ( 2.75 MeV )
High-energy neutrons can also produce tritium from lithium-7 in an endothermic reaction, consuming 2.466 MeV. This was discovered when the 1954 Castle Bravo nuclear test produced an unexpectedly high yield.
The reactions requiring high neutron energies are not attractive production methods.
Tritium is occasionally a direct product of nuclear fission, with a yield of about 0.01% (one per 10000 fissions). This means that tritium release or recovery needs to be considered in nuclear reprocessing even in ordinary spent nuclear fuel where tritium production was not a goal.
Tritium is also produced in heavy water-moderated reactors when deuterium captures a neutron. This reaction has a very small cross section (which is why heavy water is such a good neutron moderator) and relatively little tritium is produced; nevertheless, cleaning tritium from the moderator may be desirable after several years to reduce the risk of escape to the environment. Ontario Power Generation's Tritium Removal Facility can process up to 2.5 thousand tonnes (2,500 Mg) of heavy water a year, producing about 2.5 kg of tritium.
According to IEER's 1996 report about the United States Department of Energy, only 225 kg of tritium has been produced in the US since 1955. Since it is continuously decaying into helium-3, the stockpile was approximately 75 kg at the time of the report.
Tritium for American nuclear weapons was produced in special heavy water reactors at the Savannah River Site until their shutdown in 1988; with the Strategic Arms Reduction Treaty after the end of the Cold War, existing supplies were sufficient for the new, smaller number of nuclear weapons for some time. Production was resumed with irradiation of lithium-containing rods (replacing the usual boron-containing control rods) at the commercial Watts Bar Nuclear Generating Station in 2003-2005 followed by extraction of tritium from the rods at the new Tritium Extraction Facility at SRS starting in November 2006.
Lithium is widely distributed on Earth but does not naturally occur in elemental form due to its high reactivity. Estimates for crustal content range from 20 to 70 ppm by weight. In keeping with its name, lithium forms a minor part of igneous rocks, with the largest concentrations in granites. Granitic pegmatites also provide the greatest abundance of lithium-containing minerals, with spodumene and petalite being the most commercially viable sources. A newer source for lithium is hectorite clay, the only active development of which is through the Western Lithium Corporation in the United States.
According to the Handbook of Lithium and Natural Calcium, "Lithium is a comparatively rare element, although it is found in many rocks and some brines, but always in very low concentrations. There are a fairly large number of both lithium mineral and brine deposits but only comparatively a few of them are of actual or potential commercial value. Many are very small, others are too low in grade." At 20 mg lithium per kg of Earth's crust , lithium is the 25th most abundant element. Nickel and lead have the about the same abundance.
The largest reserve base of lithium is in the Salar de Uyuni area of Bolivia, which has 5.4 million tons. According to the US Geological Survey, the production and reserves of lithium in metric tons are as follows:
Contrary to the USGS data in the table, other estimates put Chile's reserve base at 7,520,000 metric tons of lithium, and Argentina's at 6,000,000 metric tons.
Seawater contains an estimated 230 billion tons of lithium, though at a low concentration of 0.1 to 0.2 ppm.
|Biosphere, oceans, atmosphere|
|0.45 × 1018 kilograms|
|Organic carbon||13.2 × 1018 kg|
|Carbonates||62.4 × 1018 kg|
|1200 × 1018 kg|
Carbon is the fourth most abundant chemical element in the universe by mass after hydrogen, helium, and oxygen. Carbon is abundant in the Sun, stars, comets, and in the atmospheres of most planets. Some meteorites contain microscopic diamonds that were formed when the solar system was still a protoplanetary disk. Microscopic diamonds may also be formed by the intense pressure and high temperature at the sites of meteorite impacts.
In combination with oxygen in carbon dioxide, carbon is found in the Earth's atmosphere (in quantities of approximately 810 gigatonnes) and dissolved in all water bodies (approximately 36,000 gigatonnes). Around 1,900 gigatonnes are present in the biosphere. Hydrocarbons (such as coal, petroleum, and natural gas) contain carbon as well—coal "reserves" (not "resources") amount to around 900 gigatonnes, and oil reserves around 150 gigatonnes. With smaller amounts of calcium, magnesium, and iron, carbon is a major component in very large masses of carbonate rock (limestone, dolomite, marble etc.).
Coal is a significant commercial source of mineral carbon; anthracite containing 92–98% carbon and the largest source (4,000 Gt, or 80% of coal, gas and oil reserves) of carbon in a form suitable for use as fuel.
Natural diamonds occur in the rock kimberlite, found in ancient volcanic "necks," or "pipes". Most diamond deposits are in Africa, notably in South Africa, Namibia, Botswana, the Republic of the Congo, and Sierra Leone. There are also deposits in Arkansas, Canada, the Russian Arctic, Brazil and in Northern and Western Australia.
Diamonds are now also being recovered from the ocean floor off the Cape of Good Hope. However, though diamonds are found naturally, about 30% of all industrial diamonds used in the U.S. are now made synthetically.
Carbon-14 is formed in upper layers of the troposphere and the stratosphere, at altitudes of 9–15 km, by a reaction that is precipitated by cosmic rays. Thermal neutrons are produced that collide with the nuclei of nitrogen-14, forming carbon-14 and a proton.
Although magnesium is found in over 60 minerals, only dolomite( sedimentary carbonate rock and a mineral, both composed of calcium magnesium carbonate CaMg(CO3)2 found in crystals), magnesite(magnesium carbonate, MgCO3. Iron (as Fe2+) substitutes for magnesium (Mg) with a complete solution series with siderite, FeCO3), brucite(the mineral form of magnesium hydroxide, with the chemical formula Mg(OH)2), carnallite( a hydrated potassium magnesium chloride with formula: KMgCl3·6(H2O)), talc, and olivine are of commercial importance.
The Mg2+ cation is the second most abundant cation in sea water (occurring at about 12% of the mass of sodium there), which makes sea water and sea-salt an attractive commercial source of Mg. To extract the magnesium, calcium hydroxide is added to sea water to form magnesium hydroxide precipitate.
- MgCl2 + Ca(OH)2 → Mg(OH)2 + CaCl2
- Mg(OH)2 + 2 HCl → MgCl2 + 2 H2O
From magnesium chloride, electrolysis produces magnesium.
In the United States, magnesium is principally obtained by electrolysis of fused magnesium chloride from brines, wells, and sea water. At the cathode, the Mg2+ ion is reduced by two electrons to magnesium metal:
- Mg2+ + 2 e− → Mg
- 2 Cl- → Cl2 (g) + 2 e−
The United States has traditionally been the major world supplier of this metal, supplying 45% of world production even as recently as 1995. Today, the US market share is at 7%, with a single domestic producer left, US Magnesium, a company born from now-defunct Magcorp.
As of 2005, China has taken over as the dominant supplier, pegged at 60% world market share, which increased from 4% in 1995. Unlike the above-described electrolytic process, China is almost completely reliant on a different method of obtaining the metal from its ores, the silicothermic Pidgeon process (the reduction of the oxide at high temperatures with silicon).
- ↑ 1.0 1.1 Aldrich, L.T.; Nier, Alfred O. Phys. Rev. 74, 1590 - 1594 (1948). The Occurrence of He3 in Natural Sources of Helium. Page 1592, Tables I and II.
- ↑ Holden, Normen E. 1993. Helium Isotopic Abundance Variation in Nature. copy of paper BNL-49331 "Table II. 3He Abundance of Natural Gas ... 3He in ppm ... Aldrich 0.05 - 0.5 ... Sano 0.46 - 22.7", "Table V. ... of Water ... 3He in ppm ... 1.6 - 1.8 East Pacific ... 0.006 - 1.5 Manitoba Chalk River ... 164 Japan Sea" (Aldrich measured Helium from US wells, Sano that of Taiwan gas )
- ↑ WebElements Periodic Table: Professional Edition: Helium: key information
- ↑ 4.0 4.1 4.2 Smith, D.M. "any concentration of helium above approximately 0.2 percent is considered worthwhile examining" ... "U.S. government still owns approximately 1 billion nm3 of helium inventory", "Middle East and North Africa ... many very large, helium-rich (up to 0.5 percent) natural gas fields" (Smith uses nm3 to mean "normal cubic metre", elsewhere called "cubic metre at STP)
- ↑ The Mass of the Atmosphere: A Constraint on Global Analyses
- ↑ Wittenberg 1994 Page 3, Table 1. Page 9.
- ↑ Wittenberg 1994 Page A-1 citing Anderson 1993, "1200 metric tone"
- ↑ Wittenberg 1994 Page A-4 "1 kg (3He), pumping power would be 1.13x10^6MYyr ... fusion power derived ... 19 MWyr"
- ↑ Wittenberg 1994 Page A-4 using Table 1 page A-5 of US crustal natural gas
- ↑ http://afci.lanl.gov/aptnews/aptnews.mar1_98.html
- ↑ IEER: Science for Democratic Action Vol. 5 No. 1
- ↑ Wittenberg 1994
- ↑ An Evaluation of the Neutron and Gamma-ray Production Cross Sections for Nitrgoen, Los Alamos Scientific Laboratory
- ↑ IEER Tritium Report
- ↑ http://meetings.lle.rochester.edu/Tritium/documents/3.ppt
- ↑ Section 12.0 Useful Tables
- ↑ Tritium (Hydrogen-3), Human Health Fact Sheet, Argonne National Laboratory, August 2005
- ↑ Serot, O.; Wagemans, C.; Heyse, J. (2005). "New Results on Helium and Tritium Gas Production From Ternary Fission". INTERNATIONAL CONFERENCE ON NUCLEAR DATA FOR SCIENCE AND TECHNOLOGY. AIP Conference Proceedings 769: 857–860. doi:10.1063/1.1945141, http://adsabs.harvard.edu/abs/2005AIPC..769..857S.
- ↑ The Canadian Nuclear FAQ - Section D: Safety and Liability
- ↑ Tritium: The environmental, health, budgetary, and strategic effects of the Department of Energy's decision to produce tritium, Hisham Zerriffi January, 1996
- ↑ http://www.srs.gov/general/news/factsheets/tef.pdf
- ↑ Krebs, Robert E. (2006). The History and Use of Our Earth's Chemical Elements: A Reference Guide. Westport, Conn.: Greenwood Press. ISBN 0-313-33438-2.
- ↑ Cite error: Invalid
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- ↑ Moores, S. (June 2007). "Between a rock and a salt lake". Industrial Minerals 477: 58.
- ↑ Handbook of Lithium and Natural Calcium, Donald Garrett, Academic Press, 2004, cited in The Trouble with Lithium 2
- ↑ Taylor, S.R.; McLennan, S.M.; The continental crust: Its composition and evolution, Blackwell Sci. Publ., Oxford, 330 pp. (1985). Cited in Abundances of the elements (data page)
- ↑ Cite error: Invalid
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- ↑ Lithium_Microscope
- ↑ Clarke, G.M. and Harben, P.W., "Lithium Availability Wall Map". Published June 2009. Referenced at International Lithium Alliance
- ↑ "Lithium Occurrence". Institute of Ocean Energy, Saga University, Japan. Retrieved on 2009-03-13.
- ↑ Mark (1987). Meteorite Craters, University of Arizona Press.
- ↑ R. Stefanenko (1983). Coal Mining Technology: Theory and Practice, Society for Mining Metallurgy. ISBN 0895204045.
- ↑ Kasting, James (1998). "The Carbon Cycle, Climate, and the Long-Term Effects of Fossil Fuel Burning". Consequences: the Nature and Implication of Environmental Change 4 (1), http://gcrio.org/CONSEQUENCES/vol4no1/carbcycle.html.
- ↑ Vardi, Nathan (February 22, 2007). "Man With Many Enemies". Forbes.com. Retrieved on 2006-06-26.