Graduation Year

2006

Document Type

Thesis

Degree

M.S.C.E.

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Alaa Ashmawy, Ph.D.

Co-Major Professor

Maya Trotz, Ph.D.

Committee Member

Robert Carnahan, Ph.D.

Keywords

leachate, gcl, isotherm, montmorillonite, salt

Abstract

In 1986, geosynthetic clay liners (GCLs) were invented and successfully used as a replacement for the soil layer in composite lining systems. In some applications an additive (polymer) is mixed with the bentonite to increase performance, especially in those that have low concentrations of sodium bentonite (EPA 2001).Studies showing significant increases in hydraulic conductivity values for bentonite in the presence of high salt concentrations are frequently documented and there is a risk of early breakthrough due to performance failure of the GCL clay component. (Ashmawy et al, 2002). It has also been stated that sodium, potassium, calcium, and magnesium have such a high affinity for the clay's surface other chemical species have little chance of attenuation (EPA 2001).

For these reasons, researching sorption in the presence of major salt cations and polymers gains great importance.Distribution coefficients were extrapolated from Linear, Freundlich and Langmuir sorption isotherms for sodium and calcium cations modeled from data collected from batch tests of sodium bentonite and various manufactured and custom mixed polymer modified bentonites. Surface characterization before and after calcium or sodium solution exposure of all tested media was accomplished by use of scanning electron microscopy and energy dispersive x-ray analysis.

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