Plutonium "carbonate

Other Coordination Complexes. Because carbonate and bicarbonate are commonly found under environmental conditions in water, and because carbonate complexes Pu readily in most oxidation states, Pu carbonato complexes have been studied extensively. The reduction potentials vs the standard hydrogen electrode of Pu(VI)/(V) shifts from 0.916 to 0.33 V and the Pu(IV)/(III) potential shifts from 1.48 to -0.50 V in 1 Tf carbonate. These shifts indicate strong carbonate complexation. Electrochemistry, reaction kinetics, and spectroscopy of plutonium carbonates in solution have been reviewed (113). The solubiUty of Pu(IV) in aqueous carbonate solutions has been measured, and the stabiUty constants of hydroxycarbonato complexes have been calculated (Fig. 6b) (90). 

Barium, Halocarbons, 0200 Beryllium, Halocarbons, 0220 f Bromomethane, Metals, 0429 Chloroform, Metals, 0372 Plutonium, Carbon tetrachloride, 4888 Samarium, 1,1,2-Trichlorotrifluoroethane, 4911 Tin, Carbon tetrachloride, Water, 4912 Titanium, Halocarbons, 4919 Uranium, Carbon tetrachloride, 4923 Zirconium, Carbon tetrachloride, 4928 See also HALOCARBONS METALS... 

Several areas of research seem to merit top priority attempt to verify published stability constants of environmental interest at lower metal concentrations and higher pH determine stability constants that are not currently known, the prime example being the plutonium-carbonate system assess the interplay of complexation, hydrolysis, and polymerization at environmental pH values, as these factors are important but not well understood under neutral conditions study the complex chemistry of plutonyl(V), which some workers believe to be an important species in ground waters attempt to elucidate the nature and behavior of polymeric species with the ultimate objective of developing quantitative, reproducible expressions for dispersion, precipitation. 

For reactor fuel, the ternary uranium-plutonium-carbon monocarbide is prepared by reduction of (U, Pu)02 with graphite [FI], by melting a uranium-plutonium alloy with graphite, or by melting separately prepared individual carbides in an electric arc [K2]. Even though at low temperatures UC exists in the stoichiometric composition, the need for excess carbon for the... 

The uranium-carbon and plutonium-carbon system a thermochemical assessment, I A E A, Technical Report Series, Report 14, (1963), 44 pp.. Cited on page 3. 

The partitioning of plutonium from surface water to sediments in freshwater and marine environments depends on the equilibrium between plutonium(IV) and plutonium(V), and the interaction between plutonium(IV) in solution and plutonium sorbed onto sediment particle surfaces (NCRP 1984). Sorption onto marine clays was found to be largely irreversible (Higgo and Rees 1986). Higgo and Rees (1986) also found that the initial sorption of plutonium onto clays was effective in removing most of the plutonium species that would be able to sorb onto the clay. When sorption to carbonate marine sediments was investigated, it was found that some desorption from the surface would also occur. This behavior was due to the presence of plutonium carbonate complexes on the sediment surfaces which were sorbed less strongly than plutonium dioxide... 

Vienna Panel. (1963). The Uranium-Carbon and Plutonium-Carbon Systems, A Thermochemical Assessment, Kept. No. 14, Intern. At. Energy Agency, Vienna. 

Limited experimental work has been performed in which the solubilities of plutonium carbonates, sulfates, and phosphates have been determined at temperatures up to 300°C [27]. No substantial solubilities have been established at temperatures above 200°C. 

Fig. 6. Speciation diagram of plutonium as function of Eb and pH in aqueous solution at 25°C (a) carbonate-free (89) (b) 0.004 M total carbonate (90). Eb...

Pu(N03 ) -5H2 0 deep red plutonyl nitrate hexahydrate [19125-90-7], Pu02(N03 )2-6H2 0 coral red anhydrous plutonium(IV) sulfate [13692-89-2], Pu(S0 2i pinh or redPu(S0 2 4H20 and moss green plutonyl carbonate/ P2P2-/(9-P/, PUO2CO2 (30). 

Nuclear power reactors cause the transmutation of chemicals (uranium and plutonium) to fission products using neutrons as the catalyst to produce heat. Fossil furnaces use the chemical reaction of carbon and oxygen to produce CO2 and other wastes to produce heat. There is only one reaction and one purpose for nuclear power reactors there is one reaction but many puiposes for fossil-burning furnaces there are myriad chemical processes and purposes. 

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). ... 

In Figure 2 the solubility and speciation of plutonium have been calculated, using stability data for the hydroxy and carbonate complexes in Table III and standard potentials from Table IV, for the waters indicted in Figure 2. Here, the various carbonate concentrations would correspond to an open system in equilibrium with air (b) and closed systems with a total carbonate concentration of 30 mg/liter (c,e) and 485 mg/liter (d,f), respectively. The two redox potentials would roughly correspond to water in equilibrium wit air (a-d cf 50) and systems buffered by an Fe(III)(s)/Fe(II)(s)-equilibrium (e,f), respectively. Thus, the natural span of carbonate concentrations and redox conditions is illustrated. 

The existence of plutonium with an oxidation state of V (or VI) in neutral solutions or at high pH and in the presence of carbonate was previously observed (51). It has also been suggested that Pu(V) is the dominant oxidation state in sea-water and that Pu(VI) is rapidly reduced to Pu(V) in these waters (52). 

However, it has been concluded from sorption and diffusion experiments that plutonium exists largely in the tetravalent state (53) and clearly not as Pu(V), in the intermediate pH-range under oxic conditions and at low carbonate concentration. This would be representative of many groundwaters and also in agreement with the calculated curves of Figure 2. 

In the presence of mineral phases containing anions that would form sparingly soluble compounds (e.g. POt - and F for the lower oxidation states) an enhanced plutonium uptake due to chemisorption can be expected (57). For plutonium in the higher oxidation states the formation of anionic carbonate complexes would drastically reduce the sorption on e.g oxide and silicate surfaces. 

Sorption of plutonium (l.fixlO-11 M) and americium (2xl0-9 M) in artificial groundwater (salt concentration 300 mg/liter total carbonate 120 mg/liter Ref. 59) on some geologic minerals, quartz, biotite, o apatite, o attapulgite, montmorillonite. Dashed lines indicate the range for major minerals in igneous rocks. Experimental conditions room temperature, particle size 0.04-0.06 mm, solid/liquid ratio 6-10 g/1, aerated system, contact time 6 days. 

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. 

A number of freshwater lakes were surveyed for concentrations of plutonium, the ratio of its upper to lower oxidation states, pH, and the concentration of dissolved organic carbon (DOC), which are shown in Table 11(11). 

In experiments where Mono Lake water was acidified to remove carbonate and bicarbonate ions and again adjusted to pH 10, more than 90 percent of the soluble plutonium moved to the sediment phase. When carbonate ion concentration was restored, the plutonium returned to solution—strong evidence of the importance of inorganic carbon to solubility in that system(13). Early studies with Lake Michigan water, which has low DOC, had also implicated bicarbonate and carbonate as stabilizing ligands for plutonium at pH 8(14). This latter research characterized the soluble species as mainly anionic in character. 

Two of the study systems, Lake Michigan and Pond 3513, exhibit cyclic behavior in their concentrations of Pu(V) (Figure 2 and 3). The cycle in Lake Michigan seems to be closely coupled with the formation in the summer and dissolution in the winter of calcium carbonate and silica particles, which are related to primary production cycles in the lake(25). The experimental knowledge that both Pu(IV) and Pu(V) adsorb on calcium carbonate precipitates(20) confirms the importance of carbonate formation in the reduction of plutonium concentrations in late summer. Whether oxidation-reduction is important in this process has not been determined. 

---