FLOW PROPERTIES OF MONTMORILLONITE SUSPENDED IN WATER WITH SURFACTANT

The flow properties of montmorillonite, one of the main clay components in coal, were studied in water suspensions to clarify the origins of the Bingham flow properties of coal water slurry (CWM) in the presence of a surfactant. The addition of anionic surfactants, such as sodium poly(isoprenesulfonate) and sodium polycarbonate, significantly decreased the apparent viscosity and Bingham yield value of the montmorillonite suspension, although the latter value never became zero, even when a large quantity of surfactant was added. The amount of water bound to montmorillonite particles, measured using H-1 NMR, was found to increase with the addition of a surfactant. The Bingham yield value and the relative viscosity of the montmorillonite suspension were described by Michaels' equation, tau(B)=A(Sphi-Sphi0)3 (Eq. 6), and by the modified Brinkman's equation, eta(r) = (1 - Sphi)-k (Eq. 8), respectively. In both equations, the sum volume of montmorillonite particles and its bound water (Sphi) is correlated to the flow properties through constants A and k. A reduction of both A and k suggests two different actions of the anionic surfactants in the montmorillonite suspension. A decrease in the A value indicates a reduction of the strength of the aggregate networks of montmorillonite at a low shear rate, while a decrease in the k value shows that the shape of the effective montmorillonite particle becomes more spherical due to an increase of bound water.