Interactions between fossil resin and coal in the presence of anionic and cationic surfactants

Abstract

Interaction forces between resin spheres and a polished coal surface were measured by atomic force microscopy (AFM). Spherical resin particles, used for these measurements, were obtained from naturally occurring fossil resin present in Wasatch Plateau coal (Utah, USA) using a special preparation technique. Force measurements were made in solutions of sodium dodecyl sulfate and dodecylamine hydrochloride as a function of concentration. Electrophoresis and transmittance studies of coal and resin suspensions were performed for the same conditions as for the force measurements. As expected, for both surfactants, repulsive forces were observed. However, in 10 −5 M and 10 −4 M DDAH repulsive forces were not observed at distances from the surface beyond 10 nm. This concentration is very close to the point of zero charge (pzc) for resin and coal as determined by electrophoresis measurements. The force/radius values versus separation distance were plotted against concentration values as a 3D map. The trends observed were in very good agreement with electrophoresis and transmittance plots. The results show that the pzc and suspension stability can be estimated from AFM force measurements even for non-ideal surfaces, as typically encountered in many industrial processes.