Thorium metal reduction

Several methods are available for producing thorium metal it can be obtained by reducing thorium oxide with calcium, by electrolysis of anhydrous thorium chloride in a fused mixture of sodium and potassium chlorides, by calcium reduction of thorium tetrachloride mixed with... 

Thorium metal is generally prepared by the metallothermic reduction of its halides (Section II,A). Very high-quality metal containing a total of 250 ppm impurities has been prepared at the Ames Laboratory of the Department of Energy (98, 99). These workers reduced ThCl4 with excess Mg metal to yield a Th-Mg alloy, which was then heated in vacuo to remove the excess Mg (55) ... 

Thorium metal may be produced from its salts— usually the oxide or a hahde—by several methods that include electrolysis and reduction with calci-... 

Thorium metal also can he prepared hy thermal reduction of its hahdes with calcium, magnesium, sodium, or potassium at elevated temperatures (950°C), first in an inert atmosphere and then in vacuum. Fluoride and chloride thorium salts are commonly employed. Berzehus first prepared thorium by heating tetrachloride, ThCh, with potassium. Magnesium and calcium are the most common reductant. These metals are added to thorium halides in excess to ensure complete reduction. Excess magnesium or calcium is removed by heating at elevated temperatures in vacuum. One such thermal reduction of hahdes produces thorium sponge, which can be converted into the massive metal by melting in an electron beam or arc furnace. 

Reduction with reactive metals. As with uranium, processes for producing thorium by reduction with reactive metals have been developed starting with thorium oxide, chloride, or fluoride. To show which combinations of thorium compound and reactive metal are thermodynamically... 

Reduction of ThF4, Reduction of ThF4 by calcium is the process used to produce most of the nuclear-grade thorium metal in the United States. The process was developed by workers at the... 

Hayek et al. [1951HAY/REH] obtained products with compositions close to ThCl2 and ThCh from the reaction of thorium metal with gaseous chlorine in stoichiometric quantities while Jantsch and Homayr [1954JAN/HOM] reported the formation of ThCls as a result of the reduction of ThCh with aluminium and also, which is more surprising, from the thermal decomposition of ThCh at 673 K. As noted by Rand [1975RAN], contamination by oxygen and silica may have been serious in these experiments. 

In contrast to titanium and zirconium, the preparation of thorium metal via reduction of the oxide with calcium (method II) acquires increased importance and rivals the reduction of the tetrachloride with sodium (method I). Melt electrolysis (method III) is another possibility. Neglecting the small oxide content (up to 1%), which in any case has never been determined precisely, the metal obtained by any of the three methods is already quite pure and contains only 0.1-0.2% of other impurities. The Th prepared by the refining process (method IV), is definitely oxygen-free and should in any case yield the purest product. 

Thorium metal powder has recently been produced in the U.K. - on a scale of at least 6 kg per batch by an all-chloride electrolytic route, and information is available upon which a large-scale process could be based. Thorium tetrachloride is first produced in situ in an inert melt composed of sodium chloride and potassium chloride in eutectic proportions. Thorium dioxide and carbon are reacted with gaseous chlorine under the surface of the melt at a temperature of about 800°C in the presence of a ferric chloride catalyst. The catalyst is added as iron powder or pyrite (FeSg) in quantity equal to about 4 per cent of the weight of thoria. The ferric chloride, once formed, behaves as a chlorine carrier in the melt, by virtue of its ready reduction to ferrous chloride and subsequent rechlorination back to ferric chloride in contact with chlorine, i.e. 

By 1967 however, ORNL deemed another method suitable to remove lanthanides without also removing thorium and thus allow simpler single fluid operation. Here would also first be removed by fluorination and then the salt would undergo a series of liquid metal reductive extraction steps where a reductant (lithium and/or thorium) in a liquid bismuth solvent would trade places with various fission producfs and transuranics (TRUs). Carefully staged operation could allow separate removal of fhorium, and most fission products and the cleaned carrier salt could then be recombined with the extracted and thorium. 

Thorium metal turnings react with excess N2 at 400 to 940°C and the product Th3N4 decomposes to ThN powder in vacuum at 1500°C [15]. This technique can be used to convert commercial arc-melted round-bar Th derived from the Ca reduction process. It is a convenient preparative method when economy rather than purity of the product ThN powder is decisive. 

Gr. aktis, aktinos, beam or ray). Discovered by Andre Debierne in 1899 and independently by F. Giesel in 1902. Occurs naturally in association with uranium minerals. Actinium-227, a decay product of uranium-235, is a beta emitter with a 21.6-year half-life. Its principal decay products are thorium-227 (18.5-day half-life), radium-223 (11.4-day half-life), and a number of short-lived products including radon, bismuth, polonium, and lead isotopes. In equilibrium with its decay products, it is a powerful source of alpha rays. Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300-degrees G. The chemical behavior of actinium is similar to that of the rare earths, particularly lanthanum. Purified actinium comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.6-year half-life. It is about 150 times as active as radium, making it of value in the production of neutrons. 

Calcium metal is an excellent reducing agent for production of the less common metals because of the large free energy of formation of its oxides and hahdes. The following metals have been prepared by the reduction of their oxides or fluorides with calcium hafnium (22), plutonium (23), scandium (24), thorium (25), tungsten (26), uranium (27,28), vanadium (29), yttrium (30), zirconium (22,31), and most of the rare-earth metals (32). 

Carbides of the Actinides, Uranium, and Thorium. The carbides of uranium and thorium are used as nuclear fuels and breeder materials for gas-cooled, graphite-moderated reactors (see Nuclearreactors). The actinide carbides are prepared by the reaction of metal or metal hydride powders with carbon or preferably by the reduction of the oxides uranium dioxide [1344-57-6] UO2 tduranium octaoxide [1344-59-8], U Og, or thorium... 

In 1789 M. H. Klaproth examined pitchblende, thought at the time to be a mixed oxide ore of zinc, iron and tungsten, and showed that it contained a new element which he named uranium after the recendy discovered planet, Uranus. Then in 1828 J. J. Berzelius obtained an oxide, from a Norwegian ore now known as thorite he named this thoria after the Scandinavian god of war and, by reduction of its tetrachloride with potassium, isolated the metal thorium. The same method was subsequendy used in 1841 by B. Peligot to effect the first preparation of metallic uranium. 

Metallic thorium can be obtained by reduction of Th02 with Ca or by reduction of ThCU with Ca or Mg under an atmosphere of Ar (like Ti, finely divided Th is extremely reactive when hot). 

Calcium metal is used in the reduction of zirconium fluorides, thorium and uranium oxides to obtain the metals. 

Americium, californium, and einsteinium oxides have been reduced by lanthanum metal, whereas thorium has been used as the reductant metal to prepare actinium, plutonium, and curium metals from their respective oxides. Berkelimn metal could also be prepared by Th reduction of Bk02 or Bk203, but the quantity of berkelium oxide available for reduction at one time has not been large enough to produce other than thin foils by this technique. Such a form of product metal can be very difficult to handle in subsequent experimentation. The rate and yield of Am from the reduction at 1525 K of americium dioxide with lanthanum metal are given in Fig. 2. 

The light actinide metals (Th, Pa, and U) have extremely low vapor pressures. Their preparation via the vapor phase of the metal requires temperatures as high as 2375 K for U and 2775 K for Th and Pa. Therefore, uranium is more commonly prepared by calciothermic reduction of the tetrafluoride or dioxide (Section II,A). Thorium and protactinium metals on the gram scale can be prepared and refined by the van Arkel-De Boer process, which is described next. 

This is remarkable, since the reduction potential of Th(IV) to Th(III) recently has been estimated as —3.7 volts 73) and direct reduction of U(C5H5)4 and Pu(C5Hs)3 with potassium metal produces the actinide metals. The ei/z for naphthalene in acetonitrile is —2.63 V (nearly the same as the aLkaJi metals). Since this is much smaller than the Th(IV) to Th(III) reduction potential, it would seem to imply substantial stabilization of the +3 state by cyclopentadienide. The observed room temperature magnetic moment of Th(C 5115)3 (0.403 BM) is consistent with the Th(III) (5/ ) assignment. Thorium triscyclopentaxhenide is similar in behavior to U(C5H5)3, forms adducts with both THF and cyclohexyhso-nitrile and has been shown to be isostructural with the other tris (cyclopentadienyl) actinides and lanthanides. 

Finely-ground monazite is treated with a 45% NaOH solution and heated at 138°C to open the ore. This converts thorium, uranium, and the rare earths to their water-insoluble oxides. The insoluble residues are filtered, dissolved in 37% HCl, and heated at 80°C. The oxides are converted into their soluble chlorides. The pH of the solution is adjusted to 5.8 with NaOH. Thorium and uranium are precipitated along with small quantities of rare earths. The precipitate is washed and dissolved in concentrated nitric acid. Thorium and uranium are separated from the rare earths by solvent extraction using an aqueous solution of tributyl phosphate. The two metals are separated from the organic phase by fractional crystallization or reduction. 

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