Unsaturated transport processes in undisturbed heterogeneous porous media. II. Co-contaminants

Journal Article · · Soil Science Society of America Journal; (United States)

DOI:https://doi.org/10.2136/sssaj1993.03615995005700040013x· OSTI ID:5817011

Jardine, P M; Jacobs, G K ^[1]; O'Dell, J D ^[2]

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1. Oak Ridge National Lab., TN (United States)
2. Univ. of Tennessee, Knoxville, TN (United States)

Department of Energy facilities involved in defense-related activities have generated huge quantities of low-level radioactive mixed waste during the past several decades. The waste is composed of organically complexed contaminants, also known as co-contaminants, which are typically disposed in shallow land burial sites. The objective of this study was to provide an improved understanding of the geochemical processes controlling co-contaminant transport in heterogeneous unsaturated subsurface media. Large undisturbed columns were isolated from a proposed waste site consisting of fractured saprolitic shale, and the steady-state unsaturated transport of Co(II)EDTA[sup 2[minus]], Co(III)EDTA[sup [minus]], and SrEDTA[sup 2[minus]] was investigated at - 10 cm pressure head. Subsurface Fe and Al sources effectively dissociated the Sr-EDTA[sup 2[minus]] co-contaminant and Sr was transported as a reactive, uncomplexed species. The EDTA readily complexed with Fe and Al, resulting in significant solid-phase modification of the porous media via chelate-enhanced dissolution and redox alterations. Displacement of Co(II)EDTA[sup 2[minus]] through the subsurface media was characterized by a MnO[sub 2]-mediated oxidation of the co-contaminant with subsequent formation of Co(III)EDTA[sup [minus]]. The latter co-contaminant was an extremely stable complex that was transported through the subsurface as a single, reactive entity and exhibited an overall retardation that was similar to the uncomplexed contaminant Co[sup 2+]. 30 refs., 5 figs., 2 tabs.

• DOE Contract Number: AC05-84OR21400
• OSTI ID: 5817011
• Journal Information: Soil Science Society of America Journal; (United States), Journal Name: Soil Science Society of America Journal; (United States) Vol. 57:4; ISSN 0361-5995; ISSN SSSJD4
• Country of Publication: United States
• Language: English

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ALKALINE EARTH METAL COMPLEXES
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CHELATING AGENTS
CHEMICAL REACTIONS
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