Plutonium hydroxide solubility

Felmy A. R., Dhanpat R., Schramke J. A., and Ryan J. L. (1989) The solubility of plutonium hydroxide in dilute solution and in high-ionic-strength chloride brines. Radiochim. Acta 43, 29 - 35. 

Particularly in the case of plutonium hydroxide, the amount of plutonium solublized from an internal deposit by biological ligands depends upon the oxidation state of the deposited plutonium. The charge to ionic-radius ratio and the tendency towards hydrolysis decreases in the order32 33) ... 

Perez-Bustamante, J.A. (1965) Solubility product of tetravalent plutonium hydroxide and study of the amphoteric character of hexavalent plutonium hydroxide. 

The plutonium solubility increased in the presence of increased NaN03, NaOH, and NaA102 concentrations. According to the literature, Pu(V) should be the stable oxidation state in alkaline NOjT-NO solutions (8). It has been observed that the solubility of Pu(V) increases as tne NaOH concentration increases (8.11) probably this occured due to formation of the more soluble anionic hydroxide complexes of Pu(V) such as PuO,(OH)2 (11). Sodium nitrate and NaAlO, may have increased Pu(V) solubility through complexation. Sodium nitrate also may have increased plutonium solubility by oxidizing the less soluble Pu(IV), initially present in the tracer solids, to Pu(V). 

Neptunium and plutonium sorption behaviors were remarkably similar, implying that they had similar sorption reactions and solution species. Both NaOH and NaA102 decreased neptunium and plutonium sorption. Several explanations can be offered to rationalize this behavior. First, NaOH and NaAlO, may have reacted with the sediment minerals to yield solids of lower sorptive capacity. Aluminate ion, as an anionic species, also may have competed with the similar neptunate and plutonate anions for sorption sites. Finally, sodium hydroxide may have stabilized the hydrolyzed Np02(0H) and Pu02(0H)2" species in solution, as was shown in the solubility tests, and prevented sorption. Explanation of the effect of NaOH and NaA102 on neptunium and plutonium sorption will require further investigation. 

In summary, the solubility and sorption reactions of cobalt, strontium, neptunium, plutonium, and americium were found to be dependent on HLW compositions. Evidence revealed the formation in HLW of organic complexes of cobalt, strontium, and americium, and of hydroxide complexes of neptunium(V) and plutonium(V). Sorption reactions were dependent on radioelement complex formation and suspected waste/sediment reactions. These data can aid in assessing effects of future HLW processing operations as well as in judging the feasibility of continued storage of HLW in existing tanks. 

Despite its ability to remove much of the soluble plutonium present in body fluids, DTPA is not an exceptional chelating agent for tetravalent actinides. The formation constant of its plutonium complex is too low to displace hydroxides from the colloids and polymers of hydrolyzed plutonium or solubilize compounds such asPuC>2 at physiological pH. In addition, the inability of DTPA to completely coordinate the... 

While not the most toxic, plutonium is the most likely transuranium element to be encountered. Plutonium commonly exists in aqueous solution in each of the oxidation states from III to VI. However, under biological conditions, redox potentials, complexa-tion, and hydrolysis strongly favor Pu(IV) as the dominant species (27, 28). It is remarkable that there are many similarities between Pu(IV) and Fe(III) (Table I). These include the similar charge per ionic-radius ratios for Fe(III) and Pu(IV) (4.6 and 4.2 e/k respectively), the formation of highly insoluble hydroxides, and similar transport properties in mammals. The majority of soluble Pu(IV) present in body fluids is rapidly bound by the iron transport protein transferrin at the site which normally binds Fe(III). In liver cells, deposited plutonium is initially bound to the iron storage protein ferritin and... 

Tetravalent plutonium. Solutions of tetravalent plutonium salts are generally similar to tetravalent cerium and uranium. The fluoride PUF4, potassium complex fluoride K2PUF6, iodate Pu(I03)4, and phosphate Pu3(P04)4 are insoluble. Excess soluble hydroxides precipitate Pu(OH)4. The... 

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