Adsorption mechanism of quaternary amines by sepiolite

A series of adsorption tests examined the uptake of typical quaternary cationic surfactants, dodecyltrimethylammonium bromide and hexadecyltrimethylammonium bromide from water by a clay mineral, sepiolite. Adsorption tests conducted under different conditions revealed that sepiolite is highly receptive to adsorption of cationic surfactants. Adsorption of cationic surfactants on sepiolite exhibits two distinct regions. The first stage is characterized by low rate and is governed through an ion-exchange process between ammonium ions and magnesium ions in the octahedral sheet. The second stage is ascribed to a combination of chain-chain interactions through van der Waals forces and ion-exchange process. The incorporation of surfactant ion is elaborated on the basis of experimental data and thermodynamic equations.