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Impact of Ionic Strength on Colloid Mobility in Saturated And Unsaturated Porous Media

Published online by Cambridge University Press:  10 February 2011

A. P. Gamerdinger
Affiliation:
Department of Chemistry, Washington State University, Tri-Cities, Richland
D. I. Kaplan
Affiliation:
Westinghouse Savannah River Company, Aiken, SC 29808 WA 99352
J. H. H.
Affiliation:
EPRI, Inc., Palo Alto, CA 94304.
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Abstract

A model system consisting of well-characterized quartz sand, negatively charged carboxyl-modified latex microspheres, and synthetic J- 13 groundwater was used as a first-step in defining limiting conditions for colloid transport at the proposed Yucca Mountain Repository for radioactive waste. Colloid (280-nm diameter) and tracer (bromide) transport was determined using column methods under steady-state flow conditions for both saturated and unsaturated moisture conditions. Experiments were conducted at three water contents (13%, 70%, and 100% saturated) and four ionic strengths (deionized water, and 0.1 x, 1x, and 10x the ionic strength of J-13 groundwater, which has an ionic strength of 0.0116). Colloid mobility in the 13% saturated columns was appreciably less than in the 70% and 100% saturated columns, whereas colloid mobility in the 70% and 100% saturated columns were quite similar. Ionic strength had a significant impact on colloid retention, becoming more pronounced in the drier systems. Colloids were mobile in deionized water and the 0.1x J-13 groundwater. Retention was approximately 20% in lx J-13 groundwater and 100% in the 10x J-13 groundwater. Compared with the 70% and 100% saturated conditions, colloid mobility decreased for the 10% saturated condition, with greater than 50% retention for the 1x J-13 groundwater system. As observed for the 70% and 100% saturated conditions, colloids in the 10x J-13 solution were essentially immobile. Colloid mobility is greatly affected by the ionic strength of the soil solution and this effect is moisture saturation dependent.

Type
Research Article
Copyright
Copyright © Materials Research Society 1999

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References

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