Uranium association with corroding carbon steel surfaces

Abstract

We investigated the association of uranium with clean and corroded surfaces of 1010 carbon steel. Studying steel contaminated by uranium species will have an important effect on the development of methods used to clean radioactively contaminated metal waste. X-ray photoelectron spectroscopy, synchrotron infrared microspectroscopy and laboratory-based Fourier transform infrared analysis of steel surfaces exposed to uranyl nitrate showed the presence of crystallized hydrated uranyl oxides, uranyl hydroxides, iron oxyhydroxides and iron oxides. In general, heavily corroded areas physically shield the uranium species, which tended to associate spatially with hydroxyl groups and lepidocrocite. Lightly corroded areas contained uranium species with stronger axial U-O bonding. Infrared spectroscopy, Rutherford backscattering spectroscopy and energy-dispersive spectroscopy mapping analysis revealed that the uranium species are well distributed within the upper micron of the thick corrosion layer and associated more with areas of high hydroxide content. Parameters such as the concentration of uranyl nitrate solution used to expose the carbon steel coupons, the method of contamination (dipped or sprayed with dilute uranyl nitrate solution) and the degree of corrosion (accelerated corrosion before and/or after contamination) played significant roles in the distribution and nature of the uranyl hydroxide/iron oxyhydroxide corrosion products found on the surface of all coupons. These factors must be considered in the development and optimization of decontamination processes for metal waste.

Mechanism of uranium removal from the aqueous solution by elemental iron

“…U(VI) was therefore enclosed in the matrix of precipitating iron oxides and was not available for desorption with Na 2 CO 3 . The co-precipitation reaction of U(VI) with iron oxides was well described in another context by Dodge et al [53] , Duff et al [54] , and Eng et al [55] The extent of U(VI) co-precipitation by corrosion products of carbon steel was thoroughly characterized by another research group. [53,55] These authors also report about a differential recovery efficiency of surface-sorbed and co-precipitated U(VI).…”

Investigating the Mechanism of Uranium Removal by Zerovalent Iron

“…The sorbed U(VI) is then entrapped in the matrix of aging corrosion products: this is the process of co-precipitation. [28,34] Iron corrosion products are mainly porous iron oxides through which reductants such as Fe 2+ , H 2 or H can diffuse and induce abiotic reduction of sorbed U(VI). The result of this suggests that reported U(VI) reduction in the presence of ZVI under anoxic conditions is the result of a surface catalyzed reaction of iron(II).…”

“…[23][24][25][26][27] Furthermore, pollutant coprecipitation with corrosion products has been demonstrated as another removal pathway. [28,29] Therefore there are at least three possible immobilization pathways for several pollutants: reduction by Fe°, by Fe 2+ and coprecipitation with corrosion products. To be able to optimise the functionality of a ZVI wall, the actual main removal pathway for each pollutant has to be identified.…”

Incorporation of Oxidized Uranium into Fe (Hydr)oxides during Fe(II) Catalyzed Remineralization

“…Investigations of U(VI) reaction with Fe(0) provide further evidence for the importance of the iron co-precipitation pathway for the uptake of U [27]. Infrared analysis indicates U associated with Fe (hydr)oxide corrosion products is probably co-precipitated as a U-Fe (hydr)oxide phase [27,28].…”

“…Investigations of U(VI) reaction with Fe(0) provide further evidence for the importance of the iron co-precipitation pathway for the uptake of U [27]. Infrared analysis indicates U associated with Fe (hydr)oxide corrosion products is probably co-precipitated as a U-Fe (hydr)oxide phase [27,28]. Thus, both field and laboratory studies indicate that co-precipitation of U(VI) with crystalline Fe oxides formed during biotic or abiotic transformation of Fe (hydr)oxides maybe a natural attenuation pathway that can be stable on geologic time scales.…”