Adsorption of Quinoline to Kaolinite and Montmorillonite

Adsorption of quinoline (pKa 5 4.92) and background electrolyte (CaCl2) onto specimen kaolinite and montmorillonite were measured as a function of pH (3–7.5) and ionic strength (1–10 mM), and as a function of quinoline concentration (0.2–1.55 mM) at fixed pH values of maximum adsorption. Maximum sorption of quinoline occurred at pH 3.5–4.0 for kaolinite, and pH 3.0–5.0 for montmorillonite. At their respective pH values of maximum adsorption, the sorption capacity for quinoline was 100 times greater with montmorillonite than kaolinite on a mass basis. Selectivity coefficients, which were calculated from pH edge data, indicated selectivity for cationic quinoline (QH) over Ca21 was greater with montmorillonite (Kexc 5 27 at pH 4) compared to kaolinite (Kexc 5 1.6 at pH 4), and Kexc was not affected by ionic strength for either clay. The results indicate the important role of charged siloxane sites in the adsorption of this N-heterocyclic contaminant.