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Title: Uranium fate in Hanford sediment altered by simulated acid waste solutions

Many aspects of U(VI) behavior in sediments that are previously exposed to acidic waste fluids for sufficiently long times to induce significant changes in pH and other physical, mineralogical and chemical properties, are not well documented in the literature. For this reason, we conducted a series of macroscopic batch experiments combined with a variety of bulk characterization studies (Mössbauer and laser spectroscopy), micro-scale inspections (µ-XRF), and molecular scale interrogations (XANES) with the objectives to: i) determine the extent of U(VI) partitioning to Hanford sediments previously exposed to acidic waste simulants (pH = 2 and pH = 5) and under neutral conditions (pH = 8) at varying background solution concentrations (i.e., NaNO3); ii) determine micron-scale solid phase associated U valence state and phase identity; and iii) provide information for a plausible conceptual model of U(VI) attenuation under waste plume acidic conditions. The results of the batch experiments showed that the acid pre-treated sediment had high affinity for aqueous U(VI), which was removed from solution via two pH dependent and apparently different mechanisms (adsorption at pH = 2 and precipitation at pH = 5). The micro-scale inspections and XANES analyses confirmed that high concentration areas were rich mainly in U(VI), demonstrating thatmore » most of the added U(VI) was not reduced to U(IV). The laser spectroscopy data showed that uranyl phosphates {e.g. metaautunite [Ca(UO2)2(PO4)2•10-12H2O] and phosphuranylite [KCa(H3O)3(UO2)7(PO4)4O4•8(H2O)]} were present in the sediments. They also showed clear differences between the U bearing phases in the experiments conducted in the presence or absence of air. As a result, the data generated from these experiments will help in a better understanding of the reactions and processes that have a significant effect and/or control U mobility.« less
Authors:
 [1] ;  [2] ;  [2] ;  [2] ;  [2] ;  [2] ;  [2]
  1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States); ViZn Energy Systems, Inc., Columbia Falls, MT (United States)
  2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
OSTI Identifier:
1209862
Report Number(s):
PNNL-SA--105743
Journal ID: ISSN 0883-2927; 48263; 830403000
Grant/Contract Number:
AC05-76RL01830; AC02-06CH11357
Type:
Accepted Manuscript
Journal Name:
Applied Geochemistry
Additional Journal Information:
Journal Volume: 63; Journal Issue: C; Journal ID: ISSN 0883-2927
Publisher:
Elsevier
Research Org:
Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES U(VI) sorption; acid waste; U(VI) precipitation; Hanford sediments; Environmental Molecular Sciences Laboratory