Influence of additives, particle size, and incorporation of coarse particles on the shear rheology of concentrated Indian coal ash slurries

The aim of this study is to first obtain stable coal ash slurries using additives and understand their flow behaviour as a function of the size of coal ash particles and incorporation of coarse coal ash particles. The combination of 0.1 wt% cationic surfactant cetyltrimethyl ammonium bromide (CTAB) and 0.1 wt% sodium salicylate (NaSal) salt is used to stabilize the coal ash slurries with 60 wt% coal ash loading. The range of shear rate ( γ̇) of 10–500 s−1 is determined to be free from the artefacts of slip and Taylor vortices and, hence, found to be reliable for rheological measurements. The slurries show predominantly shear thinning flow behaviour irrespective of the size of coal ash particles. We also show that the viscosity of the slurries increases monotonically with the decrease in the size of coal ash particles. The incorporation of coarse coal ash particles results in a decrease in the viscosity until a critical coarse particle concentration of 30 wt% is reached, beyond which no significant change in viscosity is observed.