Some aspects about the adsorption of quinoline on fibrous silicates and Patagonian saponite

Adsorption of quinoline (Q, C9H7N) on aqueous suspensions of sepiolite, palygorskite and saponite was determined experimentally in a wide pH range. The enhancement of adsorption with increasing pH and some release of OH− were observed. The clay minerals showed, at short reaction times, a higher adsorption and then this decreased along the time. Displaced Mg2+ from octahedral sheet decreased when the Q adsorption happened. The surface of the mineral covered by the molecules at a 20 mM Q total concentration practically coincided with the BET surface for sepiolite and palygorskite. In the case of saponite, it coincided with the EGME surface.The obtained data suggest three possible mechanisms that could be involved in the interaction between Q and the surface of the mineral. 1) Adsorption of Q on surface sites (SiOH, AlOH, MgOH, FeOH) on the broken edges of the mineral via the donation σ of the N electron pair of the Q. 2) Adsorption via ¶ links on the external surface (sepiolite and palygorskite) and on the external and interlayer surface (saponite). 3) A process of ion exchange in which protonated Q (QH+) replaces Na+.