ACOUSTIC AND ELECTROACOUSTIC CHARACTERIZATION OF VARIABLE-CHARGE MINERAL SUSPENSIONS
MARIANNE
GUERIN1, JOHN C. SEAMAN1, CHARLOTTE LEHMANN1
AND ARTHUR JURGENSON2
1The University of Georgia, Savannah River Ecology
Laboratory, Savannah River Site, Aiken, South Carolina 29802, USA
2Savannah River Technology Center, Savannah River Site, Aiken,
South Carolina 29802, USA
Abstract-Acoustic
and electroacoustic measurements of particle-size distribution (PSD) and
zeta potential (~ potential), respectively, were used to obtain in
situ measures of the effects of suspension concentration and pH on
interactions between mixed-charge clays and clay minerals from a highly
weathered sediment. Measurements were obtained in concentrated suspensions
as a function of weight fraction and as a function of pH during titrations.
Standard dispersion and centrifugation methods were used to obtain a comparative
measure of PSD. Thennogravimetric analysis and X-ray diffraction patterns
were used to obtain semi-quantitative and descriptive analyses, respectively,
of the sediment, which is composed of Fe oxide minerals, kaolinite, gibbsite,
quartz, crandallite, chlorite and traces of other clay minerals. Acoustic
measurements showed that the PSD of the clay fraction varied with suspension
concentration, and electroacoustic measurements showed the 'bulk' ~ potential
increased in absolute value as the suspension concentration decreased.
Titration results were also sensitive to suspension concentration. Acoustic
measurements indicated that the suspensions became unstable at ~pH 7.5-8.0,
as the attenuation spectra changed character near this pH and the calculated
PSD shifted to a larger particle size. This pH value is near the points
of zero charge of goethite and gibbsite, as verified by titrations on
mineral standards. The results confirm the central role oxide minerals
play in regulating clay mineral interactions in highly weathered sediments,
and indicate that the average ~ potential of a suspension may be a poor
indicator of controls on suspension stability.
Key Words:Acoustic Spectroscopy, Electroacoustic Spectroscopy,
Particle-size Distribution, PSD, Thermogravimetric Analysis, Variable-charge
Minerals, Zeta Potential
SREL Reprint #2733
Guerin, M., J. C. Seaman, C. Lehmann and A. Jurgenson. 2004. Acoustic and electroacoustic characterization of variable-charge mineral suspensions. Clays and Clay Minerals 52:158-170.
