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Title: Transport of Sr 2+ and SrEDTA 2- in Partially-Saturated and Heterogeneous Sediments

Abstract

Strontium-90 has migrated deep into the unsaturated subsurface beneath leaking storage tanks in the Waste Management Areas (WMA) at the U.S. Department of Energy's (DOE) Hanford Reservation. Faster than expected transport of contaminants in the vadose zone is typically attributed to either physical hydrologic processes such as development of preferential flow pathways, or to geochemical processes such as the formation of stable, anionic complexes with organic chelates, e.g., ethylenediaminetetraacetic acid (EDTA). The goal of this paper is to determine whether hydrological processes in the Hanford sediments can influence the geochemistry of the system and hence control transport of Sr{sup 2+} and SrEDTA{sup 2-}. The study used batch isotherms, saturated packed column experiments, and an unsaturated transport experiment in an undisturbed core. Isotherms and repacked column experiments suggested that the SrEDTA{sup 2-} complex was unstable in the presence of Hanford sediments, resulting in dissociation and transport of Sr{sup 2+} as a divalent cation. A decrease in sorption with increasing solid:solution ratio for Sr{sup 2+} and SrEDTA{sup 2-} suggested mineral dissolution resulted in competition for sorption sites and the formation of stable aqueous complexes. This was confirmed by detection of MgEDTA{sup 2-}, MnEDTA{sup 2-}, PbEDTA{sup 2-}, and unidentified Sr and Ca complexes.more » Displacement of Sr{sup 2+} through a partially-saturated undisturbed core resulted in less retardation and more irreversible sorption than was observed in the saturated repacked columns, and model results suggested a significant reservoir (49%) of immobile water was present during transport through the heterogeneous layered sediments. The undisturbed core was subsequently disassembled along distinct bedding planes and subjected to sequential extractions. Strontium was unequally distributed between carbonates (49%), ion exchange sites (37%), and the oxide (14%) fraction. An inverse relationship between mass wetness and Sr suggested that sandy sediments of low water content constituted the immobile flow regime. Our results suggested that the sequestration of Sr{sup 2+} in partially-saturated, heterogeneous sediments was most likely due to the formation of immobile water in drier regions having low hydraulic conductivities.« less

Authors:
 [1];  [2];  [2];  [2];  [2];  [2];  [2]
  1. Oak Ridge National Laboratory (ORNL)
  2. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
931718
DOE Contract Number:  
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Contaminant Hydrology; Journal Volume: 91; Journal Issue: 3-4
Country of Publication:
United States
Language:
English
Subject:
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; 12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; STRONTIUM COMPLEXES; STRONTIUM COMPOUNDS; EDTA; HANFORD RESERVATION; SEDIMENTS; SORPTION; STRONTIUM 90; STORAGE FACILITIES; LEAKS; RADIONUCLIDE MIGRATION; HYDROLOGY; GEOCHEMISTRY

Citation Formats

Pace, M. N., Mayes, Melanie, Jardine, Philip M, McKay, Larry Donald, Yin, Xiangping Lisa, Mehlhorn, Tonia L, and Liu, Qing. Transport of Sr2+ and SrEDTA2- in Partially-Saturated and Heterogeneous Sediments. United States: N. p., 2007. Web. doi:10.1016/j.jconhyd.2006.11.006.
Pace, M. N., Mayes, Melanie, Jardine, Philip M, McKay, Larry Donald, Yin, Xiangping Lisa, Mehlhorn, Tonia L, & Liu, Qing. Transport of Sr2+ and SrEDTA2- in Partially-Saturated and Heterogeneous Sediments. United States. doi:10.1016/j.jconhyd.2006.11.006.
Pace, M. N., Mayes, Melanie, Jardine, Philip M, McKay, Larry Donald, Yin, Xiangping Lisa, Mehlhorn, Tonia L, and Liu, Qing. Mon . "Transport of Sr2+ and SrEDTA2- in Partially-Saturated and Heterogeneous Sediments". United States. doi:10.1016/j.jconhyd.2006.11.006.
@article{osti_931718,
title = {Transport of Sr2+ and SrEDTA2- in Partially-Saturated and Heterogeneous Sediments},
author = {Pace, M. N. and Mayes, Melanie and Jardine, Philip M and McKay, Larry Donald and Yin, Xiangping Lisa and Mehlhorn, Tonia L and Liu, Qing},
abstractNote = {Strontium-90 has migrated deep into the unsaturated subsurface beneath leaking storage tanks in the Waste Management Areas (WMA) at the U.S. Department of Energy's (DOE) Hanford Reservation. Faster than expected transport of contaminants in the vadose zone is typically attributed to either physical hydrologic processes such as development of preferential flow pathways, or to geochemical processes such as the formation of stable, anionic complexes with organic chelates, e.g., ethylenediaminetetraacetic acid (EDTA). The goal of this paper is to determine whether hydrological processes in the Hanford sediments can influence the geochemistry of the system and hence control transport of Sr{sup 2+} and SrEDTA{sup 2-}. The study used batch isotherms, saturated packed column experiments, and an unsaturated transport experiment in an undisturbed core. Isotherms and repacked column experiments suggested that the SrEDTA{sup 2-} complex was unstable in the presence of Hanford sediments, resulting in dissociation and transport of Sr{sup 2+} as a divalent cation. A decrease in sorption with increasing solid:solution ratio for Sr{sup 2+} and SrEDTA{sup 2-} suggested mineral dissolution resulted in competition for sorption sites and the formation of stable aqueous complexes. This was confirmed by detection of MgEDTA{sup 2-}, MnEDTA{sup 2-}, PbEDTA{sup 2-}, and unidentified Sr and Ca complexes. Displacement of Sr{sup 2+} through a partially-saturated undisturbed core resulted in less retardation and more irreversible sorption than was observed in the saturated repacked columns, and model results suggested a significant reservoir (49%) of immobile water was present during transport through the heterogeneous layered sediments. The undisturbed core was subsequently disassembled along distinct bedding planes and subjected to sequential extractions. Strontium was unequally distributed between carbonates (49%), ion exchange sites (37%), and the oxide (14%) fraction. An inverse relationship between mass wetness and Sr suggested that sandy sediments of low water content constituted the immobile flow regime. Our results suggested that the sequestration of Sr{sup 2+} in partially-saturated, heterogeneous sediments was most likely due to the formation of immobile water in drier regions having low hydraulic conductivities.},
doi = {10.1016/j.jconhyd.2006.11.006},
journal = {Journal of Contaminant Hydrology},
number = 3-4,
volume = 91,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}