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

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 te chnique. Force measurements were made in solutions of sodium dodecyl sulfat e and dodecylamine hydrochloride as a function of concentration. Electropho resis and transmittance studies of coal and resin suspensions were performe d for the same conditions as for the force measurements. As expected, for b oth surfactants, repulsive forces were observed. However, in 10(-5) M and 1 0(-4) M DDAH repulsive forces were not observed at distances from the surfa ce beyond 10 nm. This concentration is very close to the point of zero char ge (pzc) for resin and coal as determined by electrophoresis measurements. The force/radius values versus separation distance were plotted against con centration values as a 3D map. The trends observed were in very good agreem ent 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 pr ocesses. (C) 1999 Elsevier Science B.V. All rights reserved.