Chemical thorium oxide

The most important minerals of the lanthanide elements are monazite (phosphates of La, Ce, Pr, Nd and Sm, as well as thorium oxide) plus cerite and gadolinite (silicates of these elements). Separation is difficult because of the chemical similarity of the lanthanides. Fractional crystallization, complex formation, and selective adsorption and elution using an ion exchange resin (chromatography) are the most successful methods. 

The chemical properties of thorium resemble those of the rare earth elements. Thorium oxides are insoluble in water and alkalis, but dissolve in acids. Th forms stable complexes with fluoride and carboxy groups. In body fluids, complexes with citrate, glutamate and transferring are formed. 

In 1899 R. B. Owens found that the conductivity produced by thorium oxide in air is erratic, and Rutherford showed that this was due to a radioactive gas, which he called thorium emanation, which was chemically inert and apparently had a high molecular weight. Radium emanation was discovered by... 

The various chemical extraction stages from ore to metal are discussed some of the intermediates arising from these stages have major industrial uses or potential uses of their own. Pure thorium oxide, for example, has been employed for many years in the manufacture of incandescent gas mantles and this is at present probably still the major outlet for thorium in any form. It is antidpated that new uses will be found for most of these metals or their pure intermediates in the near future and as a result many of the process stages described will achieve a wider application. 

As far as reprocessing in the U/Pu fuel cycle is concerned, several chemical separation techniques have been proposed and developed in the past few decades. The most efficient process to date remains the PUREX process (Plutonium and Uranium Recovery by Extraction). This process uses nitric acid HNO3 and organic solvents to dissolve and extract selectively U and Pu, resulting in two separate product streams (U on one side and Pu on the other side of the process chain). As far as reprocessing in the Th/ U fuel cycle is concerned, THOREX (Thorium Oxide Recovery by Extraction) technology must be used, also based on dissolution in nitric acid and solvent extraction (however, with special care for the extraction of Pa, for the separa-tion of U and U, and for the dissolution of thorium dioxide in pure nitric acid). 

Selected properties of thorium oxide. Thorium oxide is a white, granular, slightly hygroscopic solid with a fluorite structure (lattice constant — 5.5859 0.0005) [18] and an x-ray density of 10.06. The Chemical Rubber Handbook of Chemistry and Physics [19] gives 10.03 as the density of thoria. Foex [20] gives pycnometric densities for thorium... 

Large-scale preparation of thorium oxide. In the present method (Fig. 4-3) [34] for making thorium oxide in a pilot plant operated by the Chemical Technology Division at Oak Ridge National Laboratory, 1 M... 

Fig. 4 3. Thorium oxide pilot plant chemical flowsheet. Percent yields based...

In a chemical vapor deposition (CVD) variant of conventional powder metallurgy processing, fine chromium powder is obtained by hydrogen reduction of Crl2 and simultaneously combined with fine thorium(IV) oxide [1314-20-17, H1O2, particles. This product is isostaticaHy hot pressed to 70 MPa (700 atm) and 1100°C for 2 h. Compacts are steel clad and hot roUed to sheets (24). 

About four years later in 1819, the Reverend Hans Morten Thrane Esmark (1801— 1882), an amateur mineralogist, found a black mineral in Norway and gave a sample of it to his father, a geology professor, for analysis. Unable to identify it, Professor Jens Esmark sent the sample for chemical analysis to Berzelius, who found that it contained 60% of a new type of earth oxide not recognized before. It was identified as the mineral thorite (ThSiO ). Berzelius reported his discovery in an 1829 publication and retained the name thorium, in honor of Thor, the Norse god of war. Berzelius is thus credited with thorium s discovery. 

Physical and Chemical Properties. Some of the physical and chemical properties (i.e., K°w K°<= and Henry s law constant) that are often used in the estimation of environmental fate of organic compounds are not useful or relevant for most inorganic compounds including thorium and its compounds. Relevant data concerning the physical and chemical properties, such as solubility, stability, and oxidation-reduction potential of thorium salts and complexes have been located in the existing literature. 

Uranium and thorium are actinide elements. Their chemical behavior is similar under most conditions. Both are refractory elements, both occur in nature in the +4 oxidation state, and their ionic radii are very similar (U+4 = 1.05 A, Th+4 = l.lOA). However, uranium can also exist in the +6 state as the uranyl ion (U02 2), which forms compounds that are soluble in water. Thus, under oxidizing conditions, uranium can be separated from thorium through the action of water. 

Until 1964, monazite, a thorium-rare-earth phosphate, REPO4TI13 (P04)4, was the main source for the rare-earth elements. Australia, India, Brazil. Malaysia, and the United Slates are active sources. India and Brazil supply a mixed rare-earth chloride compound after thorium is removed chemically from monazite. Bastnasite, a rare-earth fluocarbonate mineral REFCO3. is a primary source for light rare earths. From 1965 to about 1985. an open-pit resource at Mountain Pass, California, has furnished about two-thirds of world requirements for rare-earth oxides. In the early... 

The first indications of nuclear instability came from the radiation they emit as they decay. In 1896, the French scientist Henri Becquerel happened to store a sample of uranium oxide in a drawer that contained some photographic plates (Fig. 17.2). He was astonished to find that the uranium compound darkened the plates even though they were stored in a protective covering. Becquerel realized that some kind of radiation must be given off by the uranium compound he called these rays radioactivity. Marie Sklodowska Curie (Fig. 17.3), a young Polish doctoral student, showed that the radiation was independent of the state of chemical combination of the uranium. She concluded that the source must be the uranium atoms themselves. Together with her husband Pierre, she went on to show that thorium, radium, and polonium are also radioactive. 

In spite of considerable similarities between the chemical properties of lanthanides and actinides, the trivalent oxidation state is not stable for the early members of the actinide series. Due to larger ionic radii and the presence of shielding electrons, the 5f electrons of actinides are subjected to a weaker attraction from the nuclear charge than the corresponding 4f electrons of lanthanides. The greater stability of tetrapositive ions of actinides such as Th and Pu is attributed to the smaller values of fourth ionization potential for 5f electrons compared to 4f electrons of lanthanides, an effect that has been observed in aqueous solution of Th and Ce (2). Thus, thorium... 

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