Oscillatory Rheology of Three-Phase Coal Froths: Effects of Ionic Strength

The rheologic properties of a three-phase coal froth are critical to understanding the interfacial properties that are associated with its stability. Due to the fragile nature of froth, oscillatory rheology was used to make sure that the froths were not damaged during measurement. To reveal the relationship between a coal froth's rheology and its stability, oscillatory rheology was used in this study. The viscoelastic behaviors of coal froths were analyzed, which illustrated that the storage modulus (G ') of a coal froth is larger than its loss modulus (G ''), showing that coal froth is solid-like. The complex viscosity of the coal froths decreased with an increase in angular frequency, meaning that coal froth is shear-thinning. The dependence of froth rheology on ionic strength was investigated, which showed that an increase in ionic strength led to an enhancement of the storage modulus G ', as well as a decrease in tan delta (G ''/G '). The coal froths tended to be more rigid and viscous with an increase in ionic strength. The mechanism of the effect of ionic strength on froth rheology was explored using electrical double layers, cryo-SEM, and particle fractions. As the ionic strength increased, the thickness of the electrical double layer decreased, which strengthened the interaction between the particles in the froth; in addition, the solid fraction in the froth increased with an increase in the ionic strength, so the value of G ' and the froth's stability both increased.