Rheological and structural evaluation of coal slurries prepared from Indian high ash coal: role of additive addition sequence

In the present study, the influence of additive addition sequence on the interparticle interactions, surface modification, and rheological behavior of coal water slurries (CWS) was systematically investigated to enhance flowability and transport efficiency. A 52 wt.% slurry was prepared using high-ash Indian coal with a particle size range of 53–74 μm. The optimal additive pathway was identified as the sequential addition of dispersant poly (styrene sulfonic acid) sodium salt (PSS, 1 wt.%), followed by surfactant sodium dodecyl sulfate (SDS, 1 wt.%), and stabilizer xanthan gum (XG, 0.1 wt.%). Rheological measurements were conducted using an Anton Paar MCR 102 rheometer over a shear rate range of 1–1000 s−1 and a temperature range of 25–55°C. The Herschel–Bulkley model effectively described the flow behavior. In the intermediate shear rate region (10–100 s−1), the slurry prepared via the first pathway (CS-I) exhibited a significantly lower viscosity (17 mPa·s) compared to CS-II (44 mPa·s) and conventional CWS (74.6 mPa·s) at 30°C, indicating improved dispersion and reduced agglomeration. These findings were supported by FESEM, WDXRF, XRD, FTIR, and zeta potential analyses, demonstrating the importance of additive sequencing in optimizing slurry performance.