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 (τB) and plastic viscosities (ηpl) 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, τB typically decreased with increasing pH. At a given pH >5.5, both τB and ηpl increased with increasing electrolyte concentration; but for Na-illite, constant values of τB and ηpl were observed at higher electrolyte concentrations. The Na or K concentration yielding the greatest increase in τB or ηpl 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, τB 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.
Published Version
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