THE EFFECT OF THE LIQUID-SOLID INTERFACE ON THE PREPARATION AND PROPERTIES OF COAL-WATER SLURRIES

Considering coal-water slurries (CWS) as dispersed systems with a larg e separation surface, we have studied the adsorption of same species a t the solid-liquid interface; these species have been necessary for th e preparation and stabilization of coal-water-slurries (CWS). In this paper, we report the results of the study on the adsorption of polynap hthalene sulphonates (PNS) and poly-styrene sulphonates (PSS) with con trolled molecular weight and steric purity, at model coal/water interf aces and at the real coal/water once. The adsorption is Langmuir's typ e in both cases, but the interfacial distribution is different: in the case of PNS the aromatic rings are co-planar with the surface and the interactions with the pure aromatic regions of the solid surface are very strong. On the other hand, in the case of PSS the adsorption laye r is constituted by a region directly bound to the surface, and anothe r that is made up of loops and tails immersed in the aqueous solution. We report also the results obtained for the adsorption of steam onto coal; in this case water molecules result arranged in clusters on hydr ophilic sites of the surface. Finally, we report a possible model for the rheological degradation under stress for concentrated slurries. Th is degradation involves the interface and shows that the presence at t he surface of ions and polyelectrolytes used as additives is the most important factor.