Plutonium ions hydrolysis

Plutonium(IV), hydrolysis of, 19 698 Plutonium-231, 19 670 Plutonium-238, 19 668, 669, 675 special precautions for, 19 703 Plutonium-239, 19 669 Plutonium aqua ions, thermodynamic values for, 19 693t Plutonium carbide, 4 649t stoichiometry, 4 651 Plutonium carbide (2 3), 4 649t Plutonium carbides, 19 690-691 Plutonium cations, 19 692 Plutonium chalcogenides, 19 691 Plutonium complexes bonding in, 19 694—695 formation constants for, 19 697t... 

As trivalent americium has a smaller ionic potential than the ions of plutonium it hydrolyses to a much lesser extent than the various plutonium ions. However, like Pu3+, hydrolytic reactions and complex formation are still an important feature of the aqueous chemistry of Am3+. Starik and Ginzberg (25) have shown that Am(III) exists in its ionic form from pH 1.0 to pH 4.5 but above pH 4.5 hydrolysis commences and at pH 7.0 colloidal species are formed. The hydrolytic behaviour of Cm(III) resembles that of Am(III). 

Calculated concentrations of possible hydrolysis species as a function of the equilibrium pH are given in Figures 6 and 7 for americium ions and plutonium ions, respectively. In the americium solution, the predominant species at pH <7 are the Am3+ and Am(OH)2+ ions, whereas in the plutonium solution the Pu022+ ion is not the dominating species at near neutral media but polymers as postulated (Pu02)2(OH)22+ and(Pu02)3(0H)5+. 

Silver, G. L. Effect of Hydrolysis on the Disproportionation of Tetravalent and Pentavalent Plutonium Ions, U.S. AEC Report MLM-1743, Mound Laboratory, Miamisburg, OH, 1970. 

Hydrolysis. Hydrolysis is one of the most important reactions in the chemistry of plutonium in aqueous solutions. The tendency of plutonium ions to hydrolyze decreases in the order ... 

FIG. 22.5. Concentration of free plutonium ions at different oxidation states in solutions of different pH, showing the effect of hydrolysis. 

The hydrolysis thermodynamics of uranium and plutonium ions as a function of temperature have been assessed and predicted by Lemire and Tremaine [263]. 

Plutonium(III) in aqueous solution, Pu " ( 4)> is pale blue. Aqueous plutonium(IV) is tan or brown the nitrate complex is green. Pu(V) is pale red-violet or pink in aqueous solution and is beUeved to be the ion PuO Pu(VI) is tan or orange in acid solution, and exists as the ion PuO. In neutral or basic solution Pu(VI) is yellow cationic and anionic hydrolysis complexes form. Pu(VII) has been described as blue-black. Its stmcture is unknown but may be the same as the six-coordinate NpO (OH) (91). Aqueous solutions of each oxidation state can be prepared by chemical oxidants or reductants... 

Oxalates. Stable oxalates of Pu(III), Pu(IV), and Pu(VI) are known. However, only the Pu(III) and Pu(IV) oxalates are technologically important (30,147). Brilliant green plutonium(III) oxalate [56609-10-0] precipitates from nitric acid solutions containing Pu(III) ions upon addition of oxaUc acid or sodium oxalate. The composition of the precipitate isPu2(C20 2 10H2O. A homogeneous oxalate precipitation by hydrolysis of diethyl oxalate at... 

For plutonium in the tri- and tetravalent state, when hydrolysis would dominate the solution chemistry, most sorption phenomena in geologic systems can be looked upon largely as physical adsorption processes. Ion exchange processes, as defined above, would be... 

Trivalent plutonium, Pu(III), appears in many compounds. It also occurs as the Pu3+ ion which is relatively stable in solutions of medium acidity (40). It has been shown (II) that acid solution hydrolysis of Pu3+ is negligible. At a pH of about 7 the first small quantities of the hydrolysis product Pu(OH)2+ appear,... 

Pu(IV), which forms highly charged polymers, strongly sorbs to soils and sediments. Other actinide III and IV oxidation states also bind by ion exchange to clays. The uptake of these species by solids is in the same sequence as the order of hydrolysis Pu > Am(III) > U(VI) > Np(V). The uptake of these actinides by plants appears to be in the reverse order of hydrolysis Np(V) > U(VI) > Am(III) > Pu(IV), with plants showing little ability to assimilate the immobile hydrolyzed species. The further concentration of these species in the food chain with subsequent deposit in humans appears to be minor. Of the 4 tons of plutonium released to the environment in atmospheric testing of nuclear weapons, the total amount fixed in the world population is less than 1 g [of this amount, most (99.9%) was inhaled rather than ingested]. 

As with uranium, the solution chemistry is complicated, owing to hydrolysis and polynuclear ion formation, complex formation with anions other than perchlorate, and disproportionation reactions of some oxidation states. The tendency of ions to displace a proton from water increases with increasing charge and decreasing ion radius, so that the tendency to hydrolysis increases in the same order for each oxidation state, th at is, Am > Pu > Np > U and M4+ > M02+ > M3+ > M02 simple ions such as Np02OH+ or PuOH3+ are known in addition to polymeric species that in the case of plutonium can have molecular weights up to 1010. 

Hydration and Hydrolysis. The various oxidation states of plutonium form strong ion-dipole bonds with water to become strongly hydrated in aqueous solution. To a first approximation, we can expect the hydration numbers of the first coordination sphere to be the same as the most probable coordination numbers suggested in the preceeding section. This means values of 8 or 9 for Pu(lll), 7 or 8 for Pu(Vl), and, perhaps, 4 for PuOj and 6 for PuOj. However, the polarization of the water dipoles of the primary hydration layer leads to attraction of additional waters of hydration. Estimates of the total number of waters of hydration for trivalent lanthanides and actinides have been given as 12 - 15 model of a small number of... 

Determination of the stabiTity constants for EDTA chelates of plutonium(IV) is rendered difficult by hydrolysis of the metal ion at fairly low pH values and by protonation of the EDTA molecule in more strongly acid solution. Thus attempts to determine the equilibrium constant in the expression... 

All early actinides from thorium to plutonium possess a stable +4 ion in aqueous solution this is the most stable oxidation state for thorium and generally for plutonium. The high charge on tetravalent actinide ions renders them susceptible to solvation, hydrolysis, and polymerization reactions. The ions are readily hydrolyzed, and therefore act as Bronsted acids in aqueous media, and as potent Lewis acids in much of their coordination chemistry (both aqueous and nonaqu-eous). Ionic radii are in general smaller than that for comparable trivalent metal cations (effective ionic radii = 0.96-1.06 A in eight-coordinate metal complexes), but are still sufficiently large to routinely support high coordination numbers. 

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