Thorium-lead compounds

As expected from the phase diagram, the enthalpy of formation per gram-atom, 

Palenzona and Cirafici [1975PAL/C1R] have measured the enthalpy of formation of ThPb3(cr) by dynamic differential calorimetry from a mixture of the elements under experimental conditions identical to those reported for ThSu3(cr) (Section XI.4) and discussed in Appendix A. They report the value of AfN° (ThPb3, cr) = - (117 + 12) kJ-moT to be that at 298.15 K, but make no mention of any correction applied to the experimental value. For this reason, we have doubled the uncertainty stated by the authors. Nevertheless, in view of these uncertainties in processing the data, the results of [1975PAL/CIR] are quoted for information only. 

Poyarkov et al. [1976POY/LEB] have measured the solubility of thorium in Pb(l), and the thorium activities in saturated solutions, from 949 to 1043 K using the concentration cell of the type  

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Triple orthovanadates containing a divalent cation, trivalent rare earth, and tetravalent thorium or cerium, have been studied by Nabar et al. (1981 and 1983). The samples were prepared by mixing soluble compounds of the corresponding elements in water, evaporating the solution and heating at SOO C. The compounds MRTh(V04)3, where M = Ca, Cd, crystallize with the tetragonal zircon structure and those where M = Ba with the monoclinic monazite structure. Strontium and lead compounds show dimorphism (Nabar and Mhatre, 1982). 

URANIUM compounds), Pb from the thorium series, and Pb from the actinium series (see Actinides and transactinides). The crystal stmcture of lead is face-centered cubic the length of the edge of the cell is 0.49389 nm the number of atoms per unit cell is four. Other properties are Hsted in Table 1. 

Rubidium metal alloys with the other alkaU metals, the alkaline-earth metals, antimony, bismuth, gold, and mercury. Rubidium forms double haUde salts with antimony, bismuth, cadmium, cobalt, copper, iron, lead, manganese, mercury, nickel, thorium, and 2iac. These complexes are generally water iasoluble and not hygroscopic. The soluble mbidium compounds are acetate, bromide, carbonate, chloride, chromate, fluoride, formate, hydroxide, iodide. 

Coprecipitation is a partitioning process whereby toxic heavy metals precipitate from the aqueous phase even if the equilibrium solubility has not been exceeded. This process occurs when heavy metals are incorporated into the structure of silicon, aluminum, and iron oxides when these latter compounds precipitate out of solution. Iron hydroxide collects more toxic heavy metals (chromium, nickel, arsenic, selenium, cadmium, and thorium) during precipitation than aluminum hydroxide.38 Coprecipitation is considered to effectively remove trace amounts of lead and chromium from solution in injected wastes at New Johnsonville, Tennessee.39 Coprecipitation with carbonate minerals may be an important mechanism for dealing with cobalt, lead, zinc, and cadmium. 

Reduction of nitrobenzene (Grant and Streitwieser 1978, Todres et al. 1985) and 4-methoxy-nitrobenzene (Todres et al. 1985) by uranium, thorium, and lanthanum-di(cyclooctatetraene) complexes leads to azo compounds. Scheme 1.8 illustrates these reductive reactions using the di(cyclooctatetraene)-uranium complex as an example. 

In the environment, thorium and its compounds do not degrade or mineralize like many organic compounds, but instead speciate into different chemical compounds and form radioactive decay products. Analytical methods for the quantification of radioactive decay products, such as radium, radon, polonium and lead are available. However, the decay products of thorium are rarely analyzed in environmental samples. Since radon-220 (thoron, a decay product of thorium-232) is a gas, determination of thoron decay products in some environmental samples may be simpler, and their concentrations may be used as an indirect measure of the parent compound in the environment if a secular equilibrium is reached between thorium-232 and all its decay products. There are few analytical methods that will allow quantification of the speciation products formed as a result of environmental interactions of thorium (e.g., formation of complex). A knowledge of the environmental transformation processes of thorium and the compounds formed as a result is important in the understanding of their transport in environmental media. For example, in aquatic media, formation of soluble complexes will increase thorium mobility, whereas formation of insoluble species will enhance its incorporation into the sediment and limit its mobility. 

Pavlovskaia NA, Makeeva LG, Zel tser MR. 1974a. Excretion of radionuclides of the thorium-232 (thorium-228, radium-224, lead-212) series from a rats body during the uptake of thorium compounds in respiratory organs. Gig Sanit 9 42-45. [Russian]... 

The conversion of CO + H2 (syn-gas) to hydrocarbons and oxygenates (Fischer-Tropsch chemistry)119 is of considerable industrial importance and recently the activation and fixation of carbon monoxide in homogeneous systems has been an active area for research.120,121 The early transition elements and the early actinide elements, in particular zirconium124 and thorium,125 126 supported by two pentamethylcyclopentadienyl ligands have provided a rich chemistry in the non-catalytic activation of CO. Reactions of alkyl and hydride ligands attached to the Cp2M centers with CO lead to formation of reactive tf2-acyl or -formyl compounds.125,126 These may be viewed in terms of the resonance forms (1) and (2) shown below. 

Unlike the 4/orbitals in the lanthanides, the 5/orbitals in the earlier actinide elements are more expanded and so can be engaged in chemical bonding. This leads to a pattern of chemistry more analogous to that found in the d block, with the possibility of variable oxidation states up to the maximum possible determined by the number of valence electrons. Most thorium compounds contain Th(IV) (e.g. Th02) and... 

Fractional crystallization (or differential crystallization) is a process whereby two chemically compounds that form crystals with slightly different solubilities in some solvent (e.g., water) can be separated by a "tree-like" process. One should remember the herculean work by Marie Curie3, who by fractional crystallization isolated 0.1 g of intensely radioactive RaCl2 from 1 ton of pitchblende (a black mixture of many other salts, mainly oxides of uranium, lead, thorium, and rare earth elements). 

Although PUCI4 has been well characterized in the gas phase (51) in the temperature range 670-1025 K, all attempts to obtain tTiTs compound in the solid state have failed. Use of a plot of the difference AHf(MCl4,c) - AHf(M , aq) (, 8) as a function of the actinide ionic radii ( ) (as done above for PuFa) in the case of thorium, protactinium, uranium and neptunium yields a first path leading to aH (PuC14,c). A second path involves the extrapolation to the plutonium system of the difference AH5o n( C 4 ) ... 

Actinide nitrides are known for Th through Cm. All of the nitrides are high melting compounds with melting points of 2630 °C, 2560 °C, and 2580 °C for Th, Np, and Pu, respectively. The actinide nitrides can decompose to give N2. Thorium, uranimn, and plutonium nitrides are well known and can be used as nuclear fiiels. Fuels of this type, especially uranium and mixed uranium plutonium nitrides, can be used in lead-cooled fast reactors, which have been proposed as a possible next-generation nuclear reactor and for use in deep-sea research vehicles. 

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