Spectroscopic Evidence for Uranium Bearing Precipitates in Vadose Zone Sediments at the Hanford 300-Area Site

Abstract

Uranium (U) solid-state speciation in vadose zone sediments collected beneath the former North Process Pond (NPP) in the 300 Area of the Hanford site (Washington) was investigated using multi-scale techniques. In 30 day batch experiments, only a small fraction of total U (∼7.4%) was released to artificial groundwater solutions equilibrated with 1% pCO 2 . Synchrotron-based micro-X-ray fluorescence spectroscopy analyses showed that U was distributed among at least two types of species: (i) U discrete grains associated with Cu and (ii) O) at some U discrete grains, and muscovite at U intermediate concentration areas, were identified in synchrotron-based micro-X-ray diffraction. Scanning electron microscopy/energy dispersive X-ray analyses revealed 8-10 µm size metatorbernite particles that were embedded in C-, Al-, and Si-rich coatings on quartz and albite grains. In µ-and bulk-X-ray absorption structure (µ-XAS and XAS) spectroscopy analyses, the structure of metatorbernite with additional U-C and U-U coordination environments was consistently observed at U discrete grains with high U concentrations. The consistency of the µ-and bulk-XAS analyses suggests that metatorbernite may comprise a significant fraction of the total U in the sample. The entrapped, micrometer-sized metatorbernite particles in C-, Al-, and Si-rich coatings, along with the more soluble precipitated uranyl carbonates and uranophane, likely control the long-term release of U to water associated with the vadose zone sediments.

Multi-scale investigation of uranium attenuation by arsenic at an abandoned uranium mine, South Terras

“…[14][15][16][17] Owing to the higher solubility of uranyl-phosphate minerals compared with uranyl-arsenates (with solubility products of 10 −12.8 and 10 −49.2 for metatorbernite and metazeunerite, respectively), 24 it might be expected that arsenate end-members of this mineral family would dominate over the phosphate end-members, which is indeed observed in the Rietveld analysis of data shown in Fig. 3b, and composition inferred from interpolation of the unit cell volume of the end members.…”

“…Assuming the solid solution to follow Vegards Law, our unit cell volume suggests 18% solid solution of metatorbenite in metazeunerite. Metatorbernite has previously been reported to sequester uranium at other uranium-contaminated sites such as Hanford (USA) [14][15][16][17] and has also been reported to occur at South Terras 3 . Although the occurrence of metazeunerite at South Terras has been previously inferred, 18 to our knowledge, this study provides conclusive and verifiable evidence for this phase at the site, and indeed for any studied uranium-contaminated vadose sediments.…”

“…Although the occurrence of metazeunerite at South Terras has been previously inferred, 18 to our knowledge, this study provides conclusive and verifiable evidence for this phase at the site, and indeed for any studied uranium-contaminated vadose sediments. [14][15][16][17] In the µ-XANES analysis of the copper, uranium, arsenic particle shown in Fig. 3a, the reduced intensity of the white line, and the presence of a shoulder feature (labelled 'A', Fig.…”

Interstitial Incorporation of Plutonium into a Low-Dimensional Potassium Borate

“…During the last two decades, significant efforts have been made to better understand the incorporation of early actinide elements (namely Th, U, Np, and Pu) into a variety of mineral phases, such as calcite (7)(8)(9)(10)(11)(12)(13)(14)(15), zircon (4,(16)(17), monazite (4,(17)(18), zirconolite (4,(18)(19)(20)(21)(22), perovskite (4,22), garnet (4), pyrochlore (4,(23)(24)(25), brucite (26), and several other systems (27)(28)(29)(30). Particularly for transuranium elements (Np and Pu), it was determined that these can also be incorporated into a series of uranium-or thorium-based minerals such as brannerite (4), ianthinite (31), schoephite, becquerelite, compreignacite, and boltwoodite (32) or even synthetic phases such as Th 2-x/2 An IV x/2 (PO 4 ) 2 (HPO 4 )·H 2 O (An = U, Np, Pu) (33), ThSiO 4 (34), and Ba 3 (UO 2 ) 2 (HPO 4 ) 2 (PO 4 ) 2 (35).…”

“…This commonly occurring mechanism is termed "substitutional incorporation." For example, numerous studies indicate that trace amounts of uranium, present as both U(VI) and U(IV), can be incorporated into natural calcite (7)(8)(9)(10)(11)(12)(13)(14). U(IV) was found to have a stable location on the sites of divalent calcium (7), while U(VI) occupies mainly calcium sites along with other possible defects or disordered sites (8)(9).…”