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Rheology of Sodium and Potassium Illite Suspensions in Relation to Colloidal Stability

Dep. of Soil Science, North Carolina State Univ., Box 7619, Raleigh, NC 27695-7619

A. L. Page

Dep. of Soil and Environmental Science, Univ. of California, Riverside, CA 92521

*Corresponding author.

ABSTRACT

To further understand the colloidal behavior of clay minerals in soils, rheological properties of illite suspensions were investigated and related to colloidal stability. Using a concentric cylinder viscometer to measure shear stress as a function of shear rate, Bingham yield stresses (_B) and plastic viscosities (_pl) were determined for homoionic Na- and K-saturated illite suspensions varying in pH, NaCIO₄ or KCIO₄ concentration, and suspended solids concentration. For a given Na or K concentration, _B typically decreased with increasing pH. At a given pH >5.5, both _B and _pl increased with increasing electrolyte concentration; but for Na-illite, constant values of _B and _pl were observed at higher electrolyte concentrations. The Na or K concentration yielding the greatest increase in _B or _pl per unit increase in concentration was usually less than, but correlated with, published critical coagulation concentrations (CCCs) of Na- or K- illite. With increasing solids concentration at pH 7, _B increased curvilinearly for unstable suspensions and linearly for stable suspensions. In light of published models of non-Newtonian flow, data for unstable suspensions at pH 7 suggested that interparticle bonding energy or the number times energy of bonds within flocs was greater for K-illite in 25 mol K m^–3 than for Na-illite in 60 mol Na m^–3.

Contribution from the Dep. of Soil and Environmental Sciences, Univ. of California, Riverside and the Institute for Soil Fertility Research, Haren, the Netherlands.

Received for publication January 27, 1992.