Solubility Product of Tetravalent Plutonium Hydroxide and Study of the Amphoteric Character of Hexavalent Plutonium Hydroxide

Abstract

The solubility dependence of Pu(0H) 4 as a function of the pn of diluted equilibrating perchloric acid solutions has been studied by covering a wide interval of ps-From the experimental solubility data obtained and some theoretical implications, an attempt has been made to conciliate the extrapolated, experimentally found thermodynamic solubility product with DEBYE-HUCKELS theory on ionic effects to account for the variations observed of the apparent solubility product throughout the different experiments carried out. The study of the apparent solubility product as a function of the ionic force has evidenced the existence of important discontinuities, which have been tentatively referred to a number of hypothesis based on the variation of the ionic activities of the present species, and on the impurities characterized in the precipitate systematically used as the starting material throughout this work. Some other interesting features of Pu (OH)! connected with this investigation have been studied in detail. Since the analysis of the precipitate employed has evidenced the presence of some percent amounts of plutonyl hydroxide, a study of the amphoteric characteristics of this species could be undertaken simultaneously. The method used for the calculation of the instability constant of the amphoteric process involved has been described in detail. A single ion-exchange experiment has been carried out with the aim of getting some information on the state of plutonium in very diluted aqueous solutions. Zusammenfassung Wir untersuchten in einem weiten ^Η-Bereich die Löslichkeit von Pu(OH) 4 in verdünnten HC10 4 -Lösungen. Die Variation des experimentellen Löslichkeitsprodukts sollte mit der DEBYE-HÜCKEL-Theorie in Einklang stehen. Das scheinbare Löslichkeitsprodukt zeigt, als Funktion der Ionenstärke, bedeutende Diskontinuitäten, die wir mit Veränderungen der Ionenaktivität der Verbindung und Verunreinigungen des als Ausgangsprodukt verwendeten Niederschlags zu erklären suchen. In diesem Zusammenhang wurden weitere Eigenschaften des Pu(OH) 4 untersucht. Da das Ausgangspräparat einige Prozent Pu(VI)-hydroxid enthielt, konnte gleichzeitig dessen amphoteres Verhalten untersucht werden ; das dabei benutzte Rechen verfahren wird ausführlich angegeben. Den Zustand des Plutoniums in sehr verdünnter wässeriger Lösung untersuchten wir in einem Ionenaustausch-Experiment. RésuméNous avons étudié la solubilité du Pu(OH) 4 , en fonction du pu, dans des solutions d'acide perchlorique. La variation du produit de solubilité expérimental devrait être en accordance avec la théorie de DEBYE-HUCKEL. La variation du produit de solubilité apparent en fonction de la force ionique comporte des discontinuités importantes, que nous essayons d'expliquer par les variations de l'activité ionique des espèces présentes, et par la présence d'impuretés dans le produit de départ. D'autres propriétés du Pu(OH) 4 ont été corrélativement étudiées en détail. Puisque le matériel de départ contenait quelques pour cent d'hydroxyde de Pu(VI), nous avons pu étu...

Systematics of Hydrolysis Constants of Tetravalent Actinide Ions

“…Figures 4 and 5 present similar comparisons of the predicted solubility curves with the experimental results of Np(IV) [29][30][31][32] and Pu(IV), 15,[33][34][35][36] Rai et al 27) As shown in Figs. 4 and 5, the predicted solubility curves are again consistent with the experimental data in acidic region.…”

“…4 and 5, the predicted solubility curves are again consistent with the experimental data in acidic region. Although the data of Perez-Bustamente 35) are much higher than the predited solubility, possible disproportionation of Pu(IV) has been pointed out by Rai. 33) Similarly to the above, it is also noticed that there are some contributions of colloid formation to the observed solubility data in near neutral and higher pH region.…”

Hydrolysis of Plutonium(VI) at Variable Temperatures (283–343 K)

“…At each concentration of Pu VI , the titration curves at different temperatures start to differ from each other at pC H % 3.5, indicating that the hydrolysis of Pu VI becomes observable by potentiometry when pC H is above 3.5. After testing various combinations of the hydrolysis species suggested in the previous literature, [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]37] the best fit of the titration data was obtained by including three hydrolysis reactions [Eq. (3)- (5)] in the calculation.…”

“…Currently, such data are scarce, highly scattered for 298.15 K, and unknown for elevated temperatures. [1][2][3] A literature survey shows that a total of seventeen studies on the hydrolysis of Pu VI have previously been conducted at or near 298.15 K. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] A number of hydrolyzed species, (PuO 2 ) m (OH) n (2mÀn) + , have been postulated, including monomeric (m = 1 and n = 1, 2, 3), dimeric (m = 2 and n = 2, 3, 4, 5), trimeric (m = 3 and n = 5), and tetrameric species (m = 4 and n = 7). [2,18,19] Hydrolysis constants (*b n,m for the reaction mPuO 2 2 + +nH 2 O = (PuO 2 ) m (OH) n (2mÀn) + +nH + ) at or near 298.15 K have been reported.…”

Mound Laboratory Chemistry and Physics Progress Report, April--June 1970.

“…From this equation it can be seen that a very high potential would prevail for the system PuO=;^ "/PuOj, (OH)., at pH 0. Line 4 represents Equation 4. If the solubilized species of hexavalent plutonium PuOg(OH),-is nonexistent, and if hexavalent plutonium is not amphoteric at all, then lines 2 and 4 should be removed from Figure 1, and the potential-pH diagram should contain only line 1 and line 3 and its dotted extension.…”