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Sodium/Calcium-Montmorillonite Suspension and Light Scattering

Institute of Soils and Water, Volcani Center, Agricultural Research Organization (ARO), P.O. Box 6, Bet Dagan, Israel

*Corresponding author (vwrmen{at}volcani.agri.gov.il).

ABSTRACT

Light scattering method was used to determine clay concentration in aqueous suspensions. Because light scattering of nonabsorbing solid particles in suspension depends on particle size and shape in addition to the particles' concentration, these two factors should be considered in determination of clay concentration in suspension. this study was conducted to determine the effect of adsorbed ion composition and clay particle size and shape on light scattering of montmorillonite suspensions. Light scattering of montmorillonite suspensions at various particle size, clay concentrations, and equivalent fraction of exchangeable sodium (EFES) was determined at a wavelength of 550 nm. Light scattering of montmorillonite suspensions depended strongly on particle size and EFES. The scattered light intensity decreased as the particle size of the clay platelets decreased and dropped sharply with increasing EFES in the range below 0.2. The relative number of particles in a given volume of suspension at any given EFES value was smaller than predicted by the theory. This deviation indicated that Rayleigh's theory is not valid for such systems. Clay concentration, therefore, cannot be adequately determined by light scattering when changes in ionic composition and electrolyte concentration alter the particle size and shape of montmorillonite in aqueous suspension.

Contribution from the ARO, The Volcani Center, Bet Dagan, Israel no. 1396-E, 1994 series.

Received for publication June 28, 1994.