Surface Properties of Coal Fines in Water. II. Isotherms, Electrokinetics and Chainlength Dependence for Cationic Surfactant Adsorption

Abstract

The adsorption of the cationic surfactants, dodecylpyridinium chloride, tetradecyl-pyridinium bromide and hexadecylpyridinium bromide on run of mine coal at varying pH's has been studied. The effect of these surfactants on the zeta potential as a function of pH was determined. Surfactant adsorption increases in the order C₁₆ > C₁₄ > C₁₂, and generally increases with increasing pH, especially for the longer chainlengths. Microelectrophoretic zeta potential measurements clearly show the effect of surfactant adsorption, and when pH > iep, i.e. when the coal is negatively charged, charge reversal of the coal surface occurs in all cases. It is concluded that adsorption of cationic surfactants involves both electrostatic (headgroup) and hydro-phobic (alkyl chain) interactions with the coal surface.