The performance and dispersing mechanism of anionic dispersants in slurries prepared by upgraded coal

It remains a significant subject on preparing high concentrated coal water slurry (CWS) from low quality coals to address the raw material supply for slurry preparation. The performance and dispersing mechanism of anionic dispersants in slurries prepared by upgraded coal, which was refined from a low quality coal, had been investigated systematically. The rheological behaviors of CWS prepared with each dispersant, i.e. sodium lignosulfonate (SLF), naphthalene sulfonate formaldehyde (NSF) and sodium polystyrene sulfonate (PSS), were studied at first; afterwards the governing factors on slurry concentration improvement and dispersion mechanism of coal particles modified by dispersant were investigated. The results illustrated that the maximum coal loading of CWS prepared with SLF, NSF and PSS were 67%, 70% and 68%, respectively, which suggested that the improvement of slurry concentration by each dispersant was NSF > PSS > SLF. According to the surface tension, yield stress and UV measurement, the effect of dispersants on slurry concentration improvement mainly relied on the adsorption by coal particles instead of surface tension reduction on solvent or its inherent steric hindrance. Subsequently, the contact angle and zeta potential analysis further indicated the excellent dispersing performance obtained by anionic dispersant was mainly attributed to the enhancement of zeta potential instead of wetting property on coal surface. The Derjaguin-Landau-Verwey-Overbeek (DLVO) calculations revealed that the electrostatic repulsion energy was improved significantly among coal particles after dispersant adsorption. A model on dispersion mechanism by anionic dispersants has been proposed. These results demonstrated that the promotion effect on slurry concentration by anionic dispersant in CWS was mainly attributed to enhancement on electrostatic repulsive force among upgraded coal particles.