Thorium occurrence

R. Ditz and co-workers, eds., Gmelin Handbook of Inorganic Chemistg, Thorium, Suppl Hoi A1a, Natural Occurrence, Minerals (Excluding Silicates), Springer-Vedag, Berlin, 1990. 

Compounds with Sc, Y, lanthanoids and actinoids are of three types. Those with composition ME have the (6-coordinated) NaCl structure, whereas M3E4 (and sometimes M4E3) adopt the body-centred thorium phosphide structure (Th3P4) with 8-coordinated M, and ME2 are like ThAsi in which each Th has 9 As neighbours. Most of these compounds are metallic and those of uranium are magnetically ordered. Full details of the structures and properties of the several hundred other transition metal-Group 15 element compounds fall outside the scope of this treatment, but three particularly important structure types should be mentioned because of their widespread occurrence and relation to other structure types, namely C0AS3,... 

The last reaction is the most favored of these three. The actual occurrence of the reactions with elemental phosphorus or phosphorous trichloride as products has been explained to be due to kinetic reasons. The thorium present in the ore volatilizes in the form of thorium tetrachloride (ThCl4) vapor other metallic impurities such as iron, chromium, aluminum, and titanium also form chlorides and vaporize. The product obtained after chlorination at 900 °C is virtually free from thorium chloride and phosphorous compounds, and also from the metals iron, aluminum, chromium, and titanium. 

The four isotopes, as those of any element, have the same chemical properties. The four are not, however, uniformly distributed in the earth s crust the occurrence of three of them, in minerals and rocks, is associated with the radioactive decay of isotopes of thorium and uranium. In most minerals and rocks the relative amounts (or the isotopic ratios) of the isotopes of lead (often expressed relative to the amount of stable lead-204) are generally within well-known ranges, which are independent of the composition of the mineral or rock they are, however, directly related to the amounts of radioactive thorium and uranium isotope impurities in them. 

Iodargyrite, natural occurrence of, 22 668 Iodates, 14 374-375 Iodate solutions, 14 362 Iodic acid, 14 375 Iodide analysis, of water, 26 41 Iodide ion, 14 367-368 25 488 Iodide-refining method, 26 149 for vanadium, 25 520 Iodides, 14 374 thorium, 24 763 tungsten, 25 379-380 uranium, 25 439... 

TABLE 3-3. Percent Occurrence and the Energies of the Major Alpha and Beta Particles Emitted by Thorium Isotopes With Atomic Masses Ranging from 223 to 234 ... 

Harmsen K, De Haan FAM. 1980. Occurrence and behaviour of uranium and thorium in soil and water. Neth J Agric Sci 28 40-62. 

The occurrence of fission in uranium is due to the presence of 2llU, which makes up only 0.07% of natural uranium. Other elements including thorium, protactinium, neptunium, and plutonium are also capable of undergoing fission, and fission may be induced not only by neutrons but also by protons, deutrons, alpha particles, and even gamma rays. 

There are only a few minerals where thorium occurs as a significant constituent. The commercially important ore is the golden-brown, lanthanide phosphate, monazite [13064-1 -8/, LnPO where Ln = Ce, La, or Nd, in which thorium is generally present in a 1—15% elemental composition (7,8). Monazite is widely distributed around the world. Some deposits are quite large. Beach sands from Australia and India contain monazite from which concentrates of lanthanides, titanium, zirconium, and thorium are produced (7). The Travancore deposits in India are the most famous, and have been perhaps one of the most significant sources of commercial thorium. Additional information on the occurrence of thorium in minerals can be found in the literature (7). A review of the mineralogy of thorium is also available (9). 

The history of atomic emission spectrometry (AES) goes back to Bunsen and Kirchhoff, who reported in 1860 on spectroscopic investigations of the alkali and alkali earth elements with the aid of their spectroscope [1], The elements cesium and rubidium and later on thorium and indium were also discovered on the basis of their atomic emission spectra. From these early beginnings qualitative and quantitative aspects of atomic spectrometry were considered. The occurrence of atomic spectral lines was understood as uniequivocal proof of the presence of these elements in a mixture. Bunsen and Kirchhoff in addition, however, also estimated the amounts of sodium that had to be brought into the flame to give a detectable line emission and therewith gave the basis for quantitative analyses and trace determinations with atomic spectrometry. 

The element cerium is inseparably connected with the rare earth group, and it is generally customary to discuss it with the members of Group III. But it differs from the other rare earth elements in forming a well defined series of quadrivalent compounds, resembling thorium quite closely. Because of this relationship, as well as its greater abundance and commercial importance, it seems best to discuss certain phases of the chemistry of cerium with Group IV. The history, occurrence, extraction, and separations are discussed in Chapter VI. 

V. Thus, in a 100 g sample of tailings there was 0.179 g of Fe in the sand-sized fraction, 0.759 g in the silt 2md clay-sized fraction, and 0.003 g in aqueous solution (Table V). The leach experiments show the decreasing order of soluble constituents hsted in Table V is Fe > V > As > Se > U > Th = Mo = Cr at pH 1.2. All of the above elements show higher distributions on the silt and clay-sized material, except for Th which is distributed throughout all fractions. Thorium has the smallest enrichment factor (Table IV), which may be due to the occurrence of detrital rather than adsorbed Th. 

Chapters S, 6, and 7 take up uranium, thorium, and zirconium in that order. Each chapter discusses the physical and chemical properties of the element and its compounds, its natural occurrence, and the processes used to extract the element from its ores, purify it, and convert it to the forms most useful in nuclear technology. 

The lanthanoids resemble each other much more closely than do the members of a row of t/-block metals. The chemistry of the actinoids is more complicated, and in addition, only Th and U have naturally occurring isotopes. Studies of the transuranium elements (those with Z > 92) require specialized techniques. The occurrence of artihcial isotopes among the /-block elements can be seen from Appendix 5 all the actinoids are unstable with respect to radioactive decay (see Section 24.9), although the half-lives of the most abundant isotopes of thorium and uranium ( Th and t = 1.4 x lO and 4.5 x 10 yr respectively) are... 

Radium. Ra at. wt 226 (mass number of most stable isotope) at. no. 88 valence 2. A radioactive alkaline earth meta], Occurrence in earth s crust approx ]0-d% by wt. Natural isotopes 223, actinium X 224, thorium X 226 228, mesothorium 1. 22 Ra is a product of disintegration of uranium and is present in al] ores contg uranium. Separated in the form of a salt by P. and M. S. Curie from the pitchblende nf Joachimsthal, Bohemia Curie et at.. Compt. Rend. 127, 12]5 (1898). [soln of the element by electrolysis of an aq soln of radium chloride Curie, Debierne. ibid. 151, 523 (1910). 12 Ra iT, 6.7 years) produced by disintegration of thorium (I12Th) discovered in 1907 by O. Hahn in monazite residues from isolating thorium. Zaire (Congo) is the main producer of radium, Canada next. Clinical evaluation in... 

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