Heterocoagulation of hydrophobized particulates by ionic surfactants

Hydrophobic particulates, i.e. bubbles, precipitates, and coal particles are shown to exhibit similar isoelectric point (iep) values in the presence of ionic surfactants. While coal in anionic surfactant solutions exhibits negative zeta potentials in the entire pH region, coal in cationic surfactant solutions undergoes a charge reversal in alkaline pH. Adsorption and zeta potential measurements together with previously published results indicate that ionic surfactants adsorb on coal through hydrophobic bonding driven by entropy. Physicochemical similarities in the adsorption mechanisms of ionic surfactants onto the bubbles, precipitates, and coal particles are proposed to be responsible for the observed iep values and also heterocoagulation phenomena.