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Title: Colloid Formation at Waste Plume Fronts

Highly saline and caustic tank waste solutions containing radionuclides and toxic metals have leaked into sediments at U. S. Department of Energy (DOE) facilities such as the Hanford Site (Washington State). Colloid transport is frequently invoked to explain migration of radionuclides and metals in the subsurface. To understand colloid formation during interactions between highly reactive fluids and sediments and its impact on contaminant transport, we simulated tank waste solution (TWS) leakage processes in laboratory columns at ambient and elevated (70 C) temperatures. We found that maximum formation of mobile colloids occurred at the plume fronts (hundreds to thousands times higher than within the plume bodies or during later leaching). Concentrations of suspended solids were as high as 3 mass%, and their particle-sizes ranged from tens of nm to a few {micro}m. Colloid chemical composition and mineralogy depended on temperature. During infiltration of the leaked high Na{sup +} waste solution, rapid and completed Na{sup +} replacement of exchangeable Ca{sup 2+} and Mg{sup 2+} from the sediment caused accumulation of these divalent cations at the moving plume front. Precipitation of supersaturated Ca{sup 2+}/Mg{sup 2+}-bearing minerals caused dramatic pH reduction at the plume front. In turn, the reduced pH caused precipitation of othermore » minerals. This understanding can help predict the behavior of contaminant trace elements carried by the tank waste solutions, and could not have been obtained through conventional batch studies.« less
Authors:
; ; ; ; ;
Publication Date:
OSTI Identifier:
841063
Report Number(s):
LBNL-56059
R&D Project: G42401; TRN: US200513%%282
DOE Contract Number:
AC03-76SF00098
Resource Type:
Journal Article
Resource Relation:
Journal Name: Environmental Science and Technology; Journal Volume: 38; Journal Issue: 22; Other Information: Submitted to Environmental Science and Technology: Volume 38, No.22; Journal Publication Date: 11/15/2004; PBD: 22 May 2004
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Director. Office of Science. Office of Biological and Environmental Research (US)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; CATIONS; CHEMICAL COMPOSITION; COLLOIDS; ELEMENTS; LEACHING; LIQUID WASTES; MINERALOGY; PLUMES; PRECIPITATION; RADIOISOTOPES; SEDIMENTS; TANKS; TRACE AMOUNTS; TRANSPORT; WASTES