A. P. Novikov

Sorption of Np(V), Pu(V), and Pu(IV) on colloids of Fe(III) oxides and hydrous oxides and MnO2

AbstractSorption of Np(V), Pu(V), and Pu(IV) on colloids of synthetic goethite (α-FeOOH), hematite (α-Fe2O3), maghemite (γ-Fe2O3), and amorphous MnO2 was studied over wide ranges of solution pH and ionic strength by solvent extraction and X-ray photoelectron spectroscopy (XPS). Plutonium(V) is reduced upon sorption on α-FeOOH, but not on α-Fe2O3 and γ-Fe2O3. On the MnO2 surface, Pu occurs as Pu(VI). From the pH dependences of the actinide sorption, the equilibrium constants of the reactions of Np(V)O2+ and Pu(V)O2+ with the surface hydroxy groups of the investigated colloid particles and a set of the equilibrium constants of the reactions of Pu(IV) hydroxo complexes with α-FeOOH were obtained. If no redox reactions occur on the surface of the colloid particles, these constants decrease in the order

Hot Particles of the Second Kind in Flood Lands of the Yenisei River

K_{MnO_2 } > K_{\alpha - FeOOH} > K_{\alpha - Fe_2 O_3 } \sim K_{\gamma - Fe_2 O_3 }

Effect of Redox Conditions on Actinide Speciation and Partitioning with Colloidal Matter

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Speciation and Migration Behavior of Pu and Am in Floodplain Soils and Bottom Sediments of the Yenisei River

This paper desribes the main sources of radioactive contamination of Russia and some techniques elaborated in the V. I. Vernadsky Institute of Geochemistry and Analytical Chemistry for the determination and speciation of radionuclides in the environment. Data on radioecological monitoring of the zone affecting by Production Association “Mayak” are presented as example of the use of these techniques. Some problems of the calculation of radionuclide migration coefficients and the determination of their so called geochemical forms of occurrence are discussed.

Association of radionuclides with colloids in soil solutions

Specific modification of hot particles found in flood-land soils of the Yenisei River was studied. In contrast to the known hot particles (hot particles of the first kind), newly found hot particles are referred to as hot particles of the second kind. Abundance, radionuclide composition, and other characteristics of hot particles of the first and second kinds are compared.

Kinetics of americium and europium extraction by tert-butylthiacalix[4]arene from alkaline media

The possibilities of liquid membrane preconcentration of neptunium from environmental samples of different nature have been studied. The use the solid-supported liquid membrane containing a trioctylmethylammonium nitrate carrier allows to achieve preconcentration factors of 102–5×102. The teflon solid support does not interact with the luminescent matrix (CaF2, PbMoO4) during calcination at 900 °C, so it makes practical to measure the neptunium content by luminescence without reextraction to aqueous solution. As a result, the detection limit of neptunium is lowed down to 10−13 g ml−1 and 5×10−13 g g−1 for pure solutions and soils, respectively.

Solid-phase extraction of plutonium(IV) an americium(III) using N-benzoylphenylhydroxylamine and its derivatives

Colloid-facilitated transport of actinides in subsurface environments depends on various geochemical and geological properties among which the redox conditions are very important. In reducing conditions, redox-sensitive actinides are stabilized in low valence states and could potentially form intrinsic colloids while in oxidizing conditions, they form pseudocolloids by sorption or coprecipitation onto natural aquatic colloids. The difference in actinides’ behavior associated with colloids at two sites in Russia under different redox conditions is discussed in this chapter. Successive micro- and ultrafiltrations of groundwater samples were performed by electron microscopic methods, nanoSIMS and sequential extraction for partitioning. Under oxidizing conditions of the PA “Mayak” site (Southern Urals, Russia), U and Np are present in the higher oxidation states while Pu is mostly found in the tetravalent state. Under these conditions, actinides are bound to amorphous hydrous ferric oxide (HFO) and Mn oxides, forming pseudocolloids as demonstrated by nanoSIMS. According to nanoSIMS, at the Tomsk site (Siberian Chemical Combine, Russia) oxidizing waste solutions were mixed with reducing groundwater resulting in reduction of U(VI) and formation of intrinsic U(IV) hydroxocolloids. Most of the U and Pu in a reducing environment are present in a residual fraction of low-mobility that favors slow migration rates.

Speciation of radionuclides in colloidal matter of underground waters taken from observation wells in the zone of impact of Lake Karachai

Am and Pu speciation in floodplain soils and bottom sediments of the Yenisei River is studied. Pu is more tightly associated with amorphous hydroxides as compared to Am. Am associated with organic matter is potentially more mobile than Pu. Model experiments showed that fulvic acids decelerate Am sorption from water to floodplain soil.