Comparative study on distribution characteristics of anionic dispersants in coal water slurry

The anionic dispersants, i.e., sodium lignosulfonate (SLF), naphthalene sulfonate formaldehyde (NSF) and sodium polystyrene sulfonate (PSS), were commonly used to prepare a high concentrated coal water slurry (CWS). In order to reveal the distribution characteristics of the dispersants in CWS system and their adsorption behaviors on coal particle surface, the adsorption experiments, surface tension measurements, contact angle measurements and XPS analysis were conducted in this study. The saturation adsorption amount of dispersants on the coal surface was SLF > NSF > PSS. The fitting results showed that the three anionic dispersants were all monolayer adsorption with a chemical reaction or electron exchange. Surface tension measurements indicated that most SLF molecules were still dissolved in the liquid phase because of the lowest adsorption quantity and packing densities at the liquid-air interface. Contact angle measurements suggested that the hydrophilic groups of the dispersants were stretched to the solution. The adsorbed layer thickness of coal with different dispersants was uniform with the adsorption amount on the coal-liquid interface, which was opposed to the order of the adsorption amount on the liquid-air interface. It was concluded that there were competitive adsorptions between the liquid-air interface and the coal-liquid interface.