Rheological behavior of coal-water slurry using sodium tripolyphosphate as a dispersant

The rheological nature of coal-water suspensions of an Indian coal variety is reported in the shear rate range of 60-160 s(-1). Sodium tripolyphosphate (STPP) is used as a dispersant or chemical additive for the slurries. The effects of percentage solid loading, dispersant dosage and pH on the rheological nature are comprehensively studied. The rheological data is fitted for power-law model to categorize the slurry flow nature with reference to the calculated flow behavior index of the model. At lower solid loadings (10% 20%), the shear stress-shear rate relation did not alter with the dispersant dosage or pH and the slurries of exhibited dilatant behavior. The effects of the slurry parameters are quite predominant at higher solid loadings (30%, 40%, and 50%). For pH >= 8.0, dilatancy of the slurries were observed for 30% solids loadings with dispersant in some cases. Excluding this, the higher percent solid loadings exhibited shear thinning behavior. For a fixed shear rate, the shear stress decreased with increasing pH at higher dispersant dosages which confirms the sharp effect of pH on the slurry rheology with the dispersant addition. The increased adsorption of the anionic dispersant (STPP) on the solids at higher pH values is the reason for this trend.