Oxidation state and coordination environment of uranium in sodium iron aluminophosphate glasses

Abstract

Investigation of the oxidation state and structural positions of uranium in glasses as functions of their composition is of interest for analyzing the behavior of multivalent elements in high temperature melts and for designing glasses for immobilization of some types of radioactive waste.Whereas the state of uranium in silicate and boro silicate melts and glasses has been studied in sufficient detail (see review [1] and original articles [2][3][4][5]), the state of uranium in phosphate glasses was explored in very few articles [6][7][8]. The latter showed that sodium aluminophosphate glasses, as well as sodium (boro) silicate ones, under oxidizing glass melting conditions are dominated by U(VI) in the form of uranyl ions UO , with the U(VI) concentration decreasing with increasing glass melting temperature [6,7], whereas sodium free and low sodium iron phosphate glasses are dominated by U(IV) [8]. In this work, for the first time, we studied the oxidation state and coordination environment of uranium in high sodium iron alumi nophosphate glasses.The reference glass was chosen to be glass contain ing 40 mol % Na 2 O, 10 mol % Al 2 O 3 , 10 mol % Fe 2 O 3 and 40 mol % P 2 O 5 (Table 1, glass 2.1) to which ura nium oxides were added (above 100%). Glasses 2.1-2.6 were synthesized from NaPO 3 , Al 2 O 3 , Fe 2 O 3 , UO 2 , or UO 2 (NO 3 ) 2 ⋅ 6H 2 O (uranyl nitrate). Table 1 pre sents the calculated and actual compositions of the glasses. Mixtures of reagents were thoroughly mixed, placed in quartz crucibles, heated to 1300°С, and kept at this temperature for 30 min, after which the obtained melts were poured to a stainless steel sheet. The chemical compositions of the samples were deter mined by X ray fluorescence analysis with a PW 2400 spectrometer (Philips Analytical B.V., The Nether lands) with the Philips Super Quantitative & IQ Soft ware 2001. The X ray absorption spectra of the glasses were recorded on a Strukturnoe materialovedenie sta tion (Kurchatov synchrotron radiation source, National Research Center "Kurchatov Institute," Moscow, Russia). The X ray absorption near edge structures (XANES) and the extended X ray absorp tion fine structures (EXAFS) were studied at the L 3 absorption edge of U were recorded simultaneously in the transmission and fluorescence geometries using an FMB Oxford avalanche photodiode and two ioniza tion chambers, which were filled with air-argon mix tures to reach the optimal absorption in the chambers and installed ahead (20%) and behind (80%) the sam ple. The incident radiation was monochromatized using a butterfly crystal with a Si(220) cut. The stan dards were UO 2 and UO 3 measured under identical conditions (standard spectra).Abstract-An analysis of the X ray absorption near edge structure (XANES) and the extended X ray absorp tion fine structure (EXAFS) of uranium determined the oxidation state and coordination environment of uranium atoms in glasses containing 40 mol % Na 2 O, 10 mol % Al 2 O 3 , 10 mol % Fe 2 O 3 , and 40 mol % P 2 O 5 to which uranium oxides were added t...

Provenance of uranium particulate contained within Fukushima Daiichi Nuclear Power Plant Unit 1 ejecta material

“…The x-ray absorption near-edge structure (XANES) spectra of the particles are characterized by a broad white line that peaks at 17,176–17,177 eV, before smoothly decreasing to a minimum at 17,200 eV. This shape has been previously attributed to the U(IV) oxidation state in uranium oxides and glasses, whereas more oxidized forms, such as U(V) and U(VI), are characterized by an increasingly asymmetric shape, with an additional shoulder growing around 17,185–17,195 eV 26–28 .

Fig. 2X-ray absorption edge profiles: SR-μ-XANES fluorescence intensity plots derived from two of the U composition particles contained within the sub-mm Si-based particle, alongside that of a comparison reference UO 2 spectra, from 44

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X-ray Absorption Fine Structure (XAFS) Studies of Oxide Glasses—A 45-Year Overview

“…The XAFS technique has also been widely used to study the short-range order and electronic structure of different atomic species in nuclear waste glass materials because vitrification of high-level radioactive waste (HLW) in borosilicate glasses is used in various countries [ 136 , 137 , 138 , 139 , 140 , 141 , 142 , 143 , 144 , 145 , 146 , 147 , 148 , 149 , 150 , 151 , 152 , 153 ]. The radiation effects on the stability and durability of these waste forms have been actively pursued, and different studies have focused on the basic understanding of the radiation-damage process [ 141 ].…”

Dissolution and Vertical Transport of Uranium from Stable Mineral Forms by Plants as Influenced by the Co-occurrence of Uranium with Phosphorus

“…Depending on the redox conditions and the pH of the environment, U can exist in different forms. Uranium is predominantly found in the +6 and +4 oxidation states in the environment . In its +4 oxidation state (U­(IV)), U is less soluble and forms more stable compounds than in its +6 oxidation state (U­(VI)), which is more readily mobilized .…”

“…Uranium is predominantly found in the +6 and +4 oxidation states in the environment. 5 In its +4 oxidation state (U(IV)), U is less soluble and forms more stable compounds than in its +6 oxidation state (U(VI)), which is more readily mobilized. 6 Uranium in the soil and water also forms complexes with various ions such as sulfate, phosphate, carbonate, and hydroxide, depending on pH conditions.…”