Transuranium hydroxides

Colloids are always present in natural waters containing the transuranium elements. (Colloids are defined as particles with sizes ranging from 1 to 450 nm. These particles form stable suspensions in natural waters.) Colloids of the transuranium elements can be formed by hydrolysis of transuranium ions, or by the sorption of transuranium elements on the naturally occurring colloids. The naturally occurring colloids include such species as metal hydroxides, silicate polymers, organics (such as humates), and the like. The mobility of the transuranium elements in an aquifer is determined largely by the mobility of its pseudocolloids, that is, those colloidal species formed by the adsorption of the transuranium ions upon the naturally occurring colloids. 

The M(OR) derivatives are known now for almost all the elements of the Periodic Table (including the transuranium elements and Xenon). They are formal analogs of hydroxides but possess much higher thermal stability. Their properties are determined not only by the electronegativity of the metal atom but also by the nature of the radical — its ramification and the acidity of the corresponding alcohol, which provides their various properties. From this point of view they can be subdivided into the following groups of compounds ... 

Hydrated oxides, hydroxides and peroxides of transuranium elements... 

Hydroxides of transuranium elements (TUE) can be obtained as amorphous precipitates from aqueous solutions with certain pH values. This process is preceded by hydrolysis that can be considered as a stepwise removal of H from H2O molecules from the first coordination sphere of the TUE ions. In order to characterize hydrolytic behavior of the TUE ions, one can use hydrolysis constants according to the following reactions ... 

Solubility data for Np, Pu, and Am hydroxo compounds in the III to VI oxidation states in alkaline media were first published in 1949 by the researchers of the Manhattan Project. Later, these data were confirmed and refined by other researchers Irom different countries. In the following, we consider some data on hydroxides and peroxides of transuranium elements. 

Transuranium(III) hydroxides form from aqueous solutions at relatively high pH. Their stabilities are remarkably different. For example, Np(III) in the form of Np(OH)3 slowly oxidizes even imder anaerobic conditions [1]. Therefore, the Np(III) hydroxide has not yet been synthesized. The Pu(III) hydroxide Pu(OH)3 has a blue color. It can be prepared as an amorphous precipitate using NH4OH or NaOH. In contrast, Am(OH)3 (pink) and Cm(OH)3 (colorless) can be isolated from solution in the form of a jelly-like precipitate that, under heating, can be transformed into a frne-crystallized state. The crystallization time increases with temperature, and at 130°C (in the autoclave) may take more than one hour [2]. 

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... 

Curium — (Pierre and Marie Curie), Cm at. wt. (247) at. no. 96 m.p. 1345°C sp. gr. 13.51 (calc.) valence 3 and 4. Although curium follows americium in the periodic system, it was actually known before americium and was the third transuranium element to be discovered. It was identified by Seaborg, James, and Ghiorso in 1944 at the wartime Metallurgical Laboratory in Chicago as a result of heUum-ion bombardment of Pu in the Berkeley, California, 60-inch cyclotron. Visible amounts (30 pg) of in the form of the hydroxide, were first isolated by Werner and Perlman... 

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