Chemistry of plutonium

Plutonium presents particular problems in its study. One reason is that, since Pu is a strong o -emitter (ti = 24,100 years) and also tends to accumulate in bone and liver, it is a severe radiological poison and must be handled with extreme care. A further problem is that the accidental formation of a critical mass must be avoided. 

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The chemistry of plutonium ions in solution has been thoroughly studied and reviewed (30,94—97). Thermodynamic properties of aqueous ions of Pu are given in Table 8 and in the Uterature (64—66). The formal reduction potentials in aqueous solutions of 1 Af HCIO or KOH at 25°C maybe summarized as follows (66,86,98—100) ... 

J. M. Cleveland, The Chemistry of Plutonium, 2nd ed., American Nuclear Society, LaGrange Park, lU., 1979. 

The chemistry of plutonium is unique in the periodic table. This theme is exemplified throughout much of the research work that is described in this volume. Many of the properties of plutonium cannot be estimated accurately based on experiments with lighter elements, such as uranium and neptunium. Because massive amounts of plutonium have been and are being produced throughout the world, the need to define precisely its chemical and physical properties and to predict its chemical behavior under widely varying conditions will persist. In addition to these needs, there is an intrinsic fundamental interest in an element with so many unusual properties and with so many different oxidation states, each with its own chemistry. 

The last forty years have seen an extensive, world-wide investigation of the chemical properties of the synthetic element, plutonium. As a result, as much is known about the chemical properties of this element as is known about the chemical properties of most of the naturally occurring elements. The papers in this volume, presented at the Symposium on the Chemistry of Plutonium held during the Kansas City meeting of the American Chemical Society, in September, 1982, represent an up-dating of this large amount of information. 

Much was also learned at the Metallurgical Laboratory about the solution chemistry of plutonium during these first few years of investigation. This included elucidation of the ionic species present in aqueous solutions of different acids and determination... 

The only crystalline phase which has been isolated has the formula Pu2(OH)2(SO )3(HaO). The appearance of this phase is quite remarkable because under similar conditions the other actinides which have been examined form phases of different composition (M(OH)2SOit, M=Th,U,Np). Thus, plutonium apparently lies at that point in the actinide series where the actinide contraction influences the chemistry such that elements in identical oxidation states will behave differently. The chemistry of plutonium in this system resembles that of zirconium and hafnium more than that of the lighter tetravalent actinides. Structural studies do reveal a common feature among the various hydroxysulfate compounds, however, i.e., the existence of double hydroxide bridges between metal atoms. This structural feature persists from zirconium through plutonium for compounds of stoichiometry M(OH)2SOit to M2 (OH) 2 (S0O 3 (H20) i,. Spectroscopic studies show similarities between Pu2 (OH) 2 (SOO 3 (H20) i, and the Pu(IV) polymer and suggest that common structural features may be present. 

Tetenbaum, M. "Some Thermodynamic Aspects of the Pu-0 System" presented at the ACS Symposium on the Chemistry of Plutonium, Kansas City, September 13-15, 1982. 

Prediction of the chemistry of plutonium in near-neutral aqueous media is highly dependent on understanding reactions that may be occurring in such media. One of the most important parameters is the stability and nature of complexes formed by plutonium in its four common oxidation states. Because Pu(III), Pu(IV), and Pu(VI) are readily hydrolysed, complexation reactions generally are studied in mildly to strongly acidic media. Data determined in acid media (and frequently at high concentrations of plutonium) then are used to predict the chemical speciation of plutonium at near-neutral pH and low concentrations of the metal ion. 

Toth, L. M. Osborne, M. M. "Further Aspects of Pu(IV) Hydrous Polymer Chemistry," Symposium on the Chemistry of Plutonium, American Chemical Society Meeting, Kansas City, Missouri, September 1982. 

Considering the anion concentration ranges in natural waters (Table II) and the magnitude of the corresponding plutonium stability constants (Table III), the chemistry of plutonium, as well as that of uranium and neptunium, is almost entirely dominated by hydroxide and carbonate complexation, considering inorganic complexes only (41, 48, 49). ... 

Nelson, D. statement at Workshop on Environmental Chemistry of Plutonium, Savannah River, 1980. 

Research into the aquatic chemistry of plutonium has produced information showing how this radioelement is mobilized and transported in the environment. Field studies revealed that the sorption of plutonium onto sediments is an equilibrium process which influences the concentration in natural waters. This equilibrium process is modified by the oxidation state of the soluble plutonium and by the presence of dissolved organic carbon (DOC). Higher concentrations of fallout plutonium in natural waters are associated with higher DOC. Laboratory experiments confirm the correlation. In waters low in DOC oxidized plutonium, Pu(V), is the dominant oxidation state while reduced plutonium, Pu(III+IV), is more prevalent where high concentrations of DOC exist. Laboratory and field experiments have provided some information on the possible chemical processes which lead to changes in the oxidation state of plutonium and to its complexation by natural ligands. 

The major source of plutonium in natural waters is the atmospheric fallout from nuclear weapons tests. Fallout plutonium is ubiquitous in marine and freshwater environments of the world with higher concentrations in the northern hemisphere where the bulk of nuclear weapons testing occurred(3). Much of the research on the aquatic chemistry of plutonium takes place in marine and freshwater systems where only fallout is present. 

Environmental chemists funded by the Department of Energy have studied these sources to learn as much as they can about the chemistry of plutonium dispersed in freshwater and marine ecosystems. Much of the early work determined the concentrations in various water bodies and the distribution between water and sediment. Table I shows results of various freshwater and marine surveys(10). 

The complete chemistry of plutonium 1 iquid-to-solid conversion processes, especially peroxide and oxalate precipitation, should be further studied. Research and development of direct thermal denitration methods should also be pursued. 

The chemistry of waste treatment processes and the development of new processes are fertile areas of research work. The speciation of plutonium in basic and laundry wastes is needed. For example, if soluble plutonium complexes in basic wastes can be destroyed, perhaps ultrafiltration could replace the flocculent-carrier precipitation process. The chemistry of plutonium(VII) and of ferrites—a candidate waste treatment process—needs to be explored.(23)... 

Bulman RA (1978) Chemistry of Plutonium and the Transuranics in the Biosphere. 34 39-77 Bulman RA (1987) The Chemistry of Chelating Agents in Medical Sciences. 67 91-141 Burdett JK (1987) Some Structural Problems Examined Using the Method of Moments. 65 29-90... 

The aqueous chemistry of plutonium may well be unique in that four oxidation states co-exist in appreciable quantities. As with the trend set at NpOj, PuOJ is quite stable and its stability increases with decreasing acidity since the couples are strongly hydrogen ion dependent. 

The aqueous chemistry of plutonium is dictated by two factors its tendency to hydrolyse and its tendency to form complexes. As the plutonium ions have a high charge and relatively small ionic radius they all exhibit a strong tendency to hydrolyse quite rapidly. Kraus (9) has shown that the tendency to hydrolyse follows the order ... 

Cleveland (16) has reviewed the chemistry of plutonium complexes and at this point it is intended to discuss only a few of the more frequently encountered complexes and return to the subject during the review of complexing agents in the biosphere. 

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