Actinide elements properties

Tracer studies using 253Es show that einsteinium has chemical properties typical of a heavy trivalent, actinide element. 

Thousands of compounds of the actinide elements have been prepared, and the properties of some of the important binary compounds are summarized in Table 8 (13,17,18,22). The binary compounds with carbon, boron, nitrogen, siUcon, and sulfur are not included these are of interest, however, because of their stabiUty at high temperatures. A large number of ternary compounds, including numerous oxyhaUdes, and more compHcated compounds have been synthesized and characterized. These include many intermediate (nonstoichiometric) oxides, and besides the nitrates, sulfates, peroxides, and carbonates, compounds such as phosphates, arsenates, cyanides, cyanates, thiocyanates, selenocyanates, sulfites, selenates, selenites, teUurates, tellurites, selenides, and teUurides. 

Hamilton, J. G. (1948a). The metabolic properties of the fission products and actinide elements, Rev. Mod. Phys. 10, 718. 

Figure 5.9. Lanthanide and actinide chemical properties. A scheme is shown of the oxidation states they present in their various classes of compounds. A rough indication of a greater frequency and a higher relative stability of each state is given by the darker blackening of each box. Notice the overwhelming presence of oxidation state 3, in the lanthanides and heavy actinides, oxidation state 2 in Eu andYb and of several higher oxidation states in U and nearby elements.

The first actinide metals to be prepared were those of the three members of the actinide series present in nature in macro amounts, namely, thorium (Th), protactinium (Pa), and uranium (U). Until the discovery of neptunium (Np) and plutonium (Pu) and the subsequent manufacture of milligram amounts of these metals during the hectic World War II years (i.e., the early 1940s), no other actinide element was known. The demand for Pu metal for military purposes resulted in rapid development of preparative methods and considerable study of the chemical and physical properties of the other actinide metals in order to obtain basic knowledge of these unusual metallic elements. 

Thorium is commonly found in combination with other actinide elements, with organic and inorganic chemicals, and with acids and bases during occupational exposure. The health effects of occupational exposures to thorium on humans, therefore, cannot necessarily be attributed to thorium. The daughter products of thorium have unique properties that also add to the radiological toxicity of thorium. For further information, see the toxicological profiles on uranium, radon, and radium. 

Symbol Cf atomic number 98 atomic weight 251 (the principal isotope) californium is a transuranium radioactive actinide element electron configuration [Rn]5/i°7s2 valence state +3 most stable isotope Cf, half-life 800 years isotope properties are presented below ... 

As many physical properties of the actinide metals depend significantly on the sample purity, refining of the metals is mandatory. The choice of the refining methods is determined by the chemical reactivity of the actinide metal in the presence of the constituents of air, by high temperature reactions with crucible materials, by the specific radioactivity and the availability of the actinide elements. 

Table 8.9 Radioactive properties of some actinide elements ...

In several respects, this ranking is not unexpected low charge, high mobility ions like Ca and Sr2+ should leach more easily than the rare earth and actinide elements. Although plutonium and cerium have similar properties as pure oxides, Plutonium was found to have a higher release rate than Cerium or Curium. Obviously, much more work is needed to understand these differences than was possible with this study. 

Solid Compounds. Thousands of compounds of the actinide elements have been prepared, and the properties of some of the important binary compounds are summarized in Table 4. 

The solubility properties of curium(111) compounds are in every way similar to those of Ihe other tripositive Actinide elements and the tnpositive Lanthanide elements. Thus the fluoride and oxalate tire insoluble in acid soluliun, while the nitrate, halides, sulfate, perchlorate, and sullide are all soluble. 

Curium trifluoride cun be reduced tn Ihc metal hy healing ill 275 C in a beryllia crucible wilh barium vapor. The metal is silvery in color and has the properties of an electropositive element in common wilh the other Actinide elements. 

In the chemistry of the fuel cycle and reactor operations, one must deal with the chemical properties of the actinide elements, particularly uranium and plutonium and those of the fission products. In this section, we focus on the fission products and then chemistry. In Figures 16.2 and 16.3, we show the chemical composition and associated fission product activities in irradiated fuel. The fission products include the elements from zinc to dysprosium, with all periodic table groups being represented. 

Fly ash increases the density, decreases the permeability, and increases the leaching resistance of Ordinary Portland Cement (OPC). It is a truism that The leach resistance of solidified cement-waste systems can be improved by any process which accelerates curing, limits porosity, or chemically bonds fission product or actinide elements. (Jantzen et al., 1984). Supercritical C02 treatment of a modified Portland cement is expected to further increase the density over the untreated material, so that a reduced porosity and improved leachability should result. In addition, the high silica content of fly ash, with its well-known sorbent properties toward actinides and certain other radionuclides, enhances the immobilization characteristics. 

The lanthanide and actinide elements are located at the bottom of the periodic table in two rows separate from the rest of the elements. By atomic number, they should be located in Periods 6 and 7, but they have special properties that distinguish them from elements in those periods. Lanthanides are very similar to each other and have some industrial uses. Many of the actinides were discovered as part of the first atomic bomb experiments. They are highly radioactive and have few uses. The transuranium elements were mostly created in the laboratory and are very short-lived. 

Especially interesting in a discussion of radionuclide speciation is the behaviour of the transuranium elements neptunium, plutonium, americium and curium. These form part of the actinide series of elements which resemble the lanthanides in that electrons are progressively added to the 5f instead of the 4f orbital electron shell. The effective shielding of these 5f electrons is less than for the 4f electrons of the lanthanides and the differences in energy between adjacent shells is also smaller, with the result that the actinide elements tend to display more complex chemical properties than the lanthanides, especially in relation to their oxidation-reduction behaviour (Bagnall, 1972). The effect is especially noticeable in the case of uranium, neptunium and plutonium, the last of which has the unique feature that four oxidation states Pum, Pu, Puv and Pu are... 

The actinide elements (which are all radioactive) up to Z = 103 are listed in Table 20-1 along with some of their properties. The principal isotopes that can be obtained in macroscopic amounts are listed in Table 20-2. The significance of the term actinide series is justified by the overall agreement of the chemistry of these elements with that concept, although it is not as clearly justified as is the lanthanide concept. Note in Table 20-1 that some irregular variation in the 5f/6d electron distribution does occur. 

Table 20-1 The Actinide Elements and Some of Their Properties"... 

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